Review of Medical Microbiology and Immunology, 13th Edition

PART XIII. USMLE (NATIONAL BOARD) PRACTICE QUESTIONS

These practice questions are presented in the format used by the United States Medical Licensing Examination (USMLE) Step 1. Note that in the computerized version of the USMLE, all questions are of the “ONE-BEST-ANSWER” type. There are no questions of the “EXCEPT” or “LEAST ACCURATE” type in which you are asked to determine the one wrong answer. Nevertheless, for studying purposes, the EXCEPT or LEAST ACCURATE type of questions are excellent learning tools because they provide you with several correct statements and only one incorrect statement rather than several incorrect ones. In view of this learning advantage, many practice questions in PART XIII of this book are of the EXCEPT or LEAST ACCURATE type. However, in PART XIV, the questions in the USMLE Practice Examination are presented in the ONE-BEST-ANSWER format, and no EXCEPT type questions are used.

After the questions regarding the specific content areas (i.e., bacteriology, virology, mycology, parasitology, and immunology), there are two additional sections, one containing questions in an extended matching format and the other containing questions based on infectious disease cases. The questions in the computerized version of the USMLE have 4 to 10 answer choices. Although the format of the questions in the extended matching section of this book is different from the format used in the USMLE, the questions in this section are designed to be a highly time-effective way of transmitting the important information.

BASIC BACTERIOLOGY

DIRECTIONS (Questions 1–39): Select the ONE lettered answer that is BEST in each question.

1. Each of the following statements concerning the surface structures of bacteria is correct EXCEPT:

(A) Pili mediate the interaction of bacteria with mucosal epithelium.

(B) Polysaccharide capsules retard phagocytosis.

(C) Both gram-negative rods and cocci have lipopolysaccharide (“endotoxin”) in their cell wall.

(D) Bacterial flagella are nonantigenic in humans because they closely resemble human flagella in chemical composition.

2. Each of the following statements concerning peptidoglycan is correct EXCEPT:

(A) It has a backbone composed of alternating units of muramic acid and acetylglucosamine.

(B) Cross-links between the tetrapeptides involve D-alanine.

(C) It is thinner in gram-positive than in gram-negative cells.

(D) It can be degraded by lysozyme.

3. Each of the following statements concerning bacterial spores is correct EXCEPT:

(A) Their survival ability is based on their enhanced metabolic activity.

(B) They are formed by gram-positive rods.

(C) They can be killed by being heated to 121°C for 15 minutes.

(D) They are formed primarily when nutrients are limited.

4. Which one of the statements is the MOST accurate comparison of human, bacterial, and fungal cells?

(A) Human cells undergo mitosis, whereas neither bacteria nor fungi do.

(B) Human and fungal cells have a similar cell wall, in contrast to bacteria, whose cell wall contains peptidoglycan.

(C) Human and bacterial cells have plasmids, whereas fungal cells do not.

(D) Human and fungal cells have similar ribosomes, whereas bacterial ribosomes are significantly different.

5. Which statement is MOST accurate regarding the drug depicted in the diagram?

image

(A) It inhibits DNA synthesis.

(B) It is bacteriostatic.

(C) It binds to 30S ribosomes.

(D) It prevents formation of folic acid.

6. Each of the following statements regarding the selective action of antibiotics on bacteria is correct EXCEPT:

(A) Chloramphenicol affects the large subunit of the bacterial ribosome, which is different from the large subunit of the human ribosome.

(B) Isoniazid affects the DNA polymerase of bacteria but not that of human cells.

(C) Sulfonamides affect folic acid synthesis in bacteria, a pathway that does not occur in human cells.

(D) Penicillins affect bacteria rather than human cells because bacteria have a cell wall, whereas human cells do not.

7. Each of the following statements concerning endotoxins is correct EXCEPT:

(A) They are less toxic (i.e., less active on a weight basis) than exotoxins.

(B) They are more stable on heating than exotoxins.

(C) They bind to specific cell receptors, whereas exotoxins do not.

(D) They are part of the bacterial cell wall, whereas exotoxins are not.

8. The MAIN host defense against bacterial exotoxins is:

(A) Activated macrophages secreting proteases

(B) IgG and IgM antibodies

(C) Helper T cells

(D) Modulation of host cell receptors in response to the toxin

9. Which one of the following processes involves a sex pilus?

(A) Transduction of a chromosomal gene

(B) Transposition of a mobile genetic element

(C) Integration of a temperate bacteriophage

(D) Conjugation resulting in transfer of an R (resistance) factor

10. Each of the following statements concerning the normal flora is correct EXCEPT:

(A) The most common organism found on the skin is Staphylococcus epidermidis.

(B) Escherichia coli is a prominent member of the normal flora of the throat.

(C) The major site where Bacteroides fragilis is found is the colon.

(D) One of the most common sites where Staphylococcus aureus is found is the nose.

11. Each of the following statements concerning the mechanism of action of antimicrobial drugs is correct EXCEPT:

(A) Vancomycin acts by inhibiting peptidoglycan synthesis.

(B) Quinolones, such as ciprofloxacin, act by inhibiting the DNA gyrase of bacteria.

(C) Erythromycin is a bactericidal drug that disrupts cell membranes by a detergent-like action.

(D) Aminoglycosides such as streptomycin are bactericidal drugs that inhibit protein synthesis.

12. Each of the following statements concerning the resistance of bacteria to antimicrobial drugs is correct EXCEPT:

(A) Resistance to chloramphenicol is known to be due to an enzyme that acetylates the drug.

(B) Resistance to penicillin is known to be due to reduced affinity of transpeptidases.

(C) Resistance to penicillin is known to be due to cleavage by β-lactamase.

(D) Resistance to tetracycline is known to be due to an enzyme that hydrolyzes the ester linkage.

13. Of the following choices, the MOST important function of antibody in host defenses against bacteria is:

(A) Activation of lysozyme that degrades the cell wall

(B) Acceleration of proteolysis of exotoxins

(C) Facilitation of phagocytosis

(D) Inhibition of bacterial protein synthesis

14. Which of the following events is MOST likely to be due to bacterial conjugation?

(A) A strain of Corynebacterium diphtheriae produces a toxin encoded by a prophage.

(B) A strain of Pseudomonas aeruginosa produces β-lactamase encoded by a plasmid similar to a plasmid of another gram-negative organism.

(C) An encapsulated strain of Streptococcus pneumoniae acquires the gene for capsule formation from an extract of DNA from another encapsulated strain.

(D) A gene encoding resistance to gentamicin in the Escherichia coli chromosome appears in the genome of a bacteriophage that has infected E. coli.

15. Which one of the following BEST describes the mode of action of endotoxin?

(A) Degrades lecithin in cell membranes

(B) Inactivates elongation factor-2

(C) Blocks release of acetylcholine

(D) Causes the release of tumor necrosis factor

16. The identification of bacteria by serologic tests is based on the presence of specific antigens. Which one of the following bacterial components is LEAST likely to contain useful antigens?

(A) Capsule

(B) Flagella

(C) Exotoxins

(D) Ribosomes

17. Each of the following statements concerning bacterial spores is correct EXCEPT:

(A) Spores are formed under adverse environmental conditions such as the absence of a carbon source.

(B) Spores are resistant to boiling.

(C) Spores are metabolically inactive and contain dipicolinic acid, a calcium chelator.

(D) Spores are formed primarily by organisms of the genus Neisseria.

18. Each of the following statements concerning the mechanism of action of antibacterial drugs is correct EXCEPT:

(A) Cephalosporins are bactericidal drugs that inhibit the transpeptidase reaction and prevent cell wall synthesis.

(B) Tetracyclines are bacteriostatic drugs that inhibit protein synthesis by blocking tRNA binding.

(C) Aminoglycosides are bacteriostatic drugs that inhibit protein synthesis by activating ribonuclease, which degrades mRNA.

(D) Erythromycin is a bacteriostatic drug that inhibits protein synthesis by blocking translocation of the polypeptide.

19. Each of the following is a typical property of obligate anaerobes EXCEPT:

(A) They generate energy by using the cytochrome system.

(B) They grow best in the absence of air.

(C) They lack superoxide dismutase.

(D) They lack catalase.

20. Each of the following statements concerning the Gram stain is correct EXCEPT:

(A) Escherichia coli stains pink because it has a thin peptidoglycan layer.

(B) Streptococcus pyogenes stains blue because it has a thick peptidoglycan layer.

(C) Mycobacterium tuberculosis stains blue because it has a thick lipid layer.

(D) Mycoplasma pneumoniae is not visible in the Gram stain because it does not have a cell wall.

21. Each of the following statements concerning the killing of bacteria is correct EXCEPT:

(A) Lysozyme in tears can hydrolyze bacterial cell walls.

(B) Silver nitrate can inactivate bacterial enzymes.

(C) Detergents can disrupt bacterial cell membranes.

(D) Ultraviolet light can degrade bacterial capsules.

22. In the Gram stain, the decolorization of gram-negative bacteria by alcohol is MOST closely related to:

(A) Proteins encoded by F plasmids

(B) Lipids in the cell wall

(C) 70S ribosomes

(D) Branched polysaccharides in the capsule

23. Chemical modification of benzylpenicillin (penicillin G) has resulted in several beneficial changes in the clinical use of this drug. Which one of the following is NOT one of those beneficial changes?

(A) Lowered frequency of anaphylaxis

(B) Increased activity against gram-negative rods

(C) Increased resistance to stomach acid

(D) Reduced cleavage by penicillinase

24. Each of the following statements concerning resistance to antibiotics is correct EXCEPT:

(A) Resistance to aminoglycosides can be due to phosphorylating enzymes encoded by R plasmids.

(B) Resistance to sulfonamides can be due to enzymes that hydrolyze the five-membered ring structure.

(C) Resistance to penicillins can be due to alterations in binding proteins in the cell membrane.

(D) Resistance to cephalosporins can be due to cleavage of the β-lactam ring.

25. The effects of endotoxin include each of the following EXCEPT:

(A) Opsonization

(B) Fever

(C) Activation of the coagulation cascade

(D) Hypotension

26. Bacterial surface structures that show antigenic diversity include each of the following EXCEPT:

(A) Pili

(B) Capsules

(C) Flagella

(D) Peptidoglycan

27. The effects of antibody on bacteria include each of the following EXCEPT:

(A) Lysis of gram-negative bacteria in conjunction with complement

(B) Augmentation of phagocytosis

(C) Increase in the frequency of lysogeny

(D) Inhibition of adherence of bacteria to mucosal surfaces

28. Each of the following statements concerning exotoxins is correct EXCEPT:

(A) When treated chemically, some exotoxins lose their toxicity and can be used as immunogens in vaccines.

(B) Some exotoxins are capable of causing disease in purified form, free of any bacteria.

(C) Some exotoxins act in the gastrointestinal tract to cause diarrhea.

(D) Some exotoxins contain lipopolysaccharides as the toxic component.

29. Each of the following statements concerning bacterial and human cells is correct EXCEPT:

(A) Bacteria are prokaryotic (i.e., they have one molecule of DNA, are haploid, and have no nuclear membrane), whereas human cells are eukaryotic (i.e., they have multiple chromosomes, are diploid, and have a nuclear membrane).

(B) Bacteria derive their energy by oxidative phosphorylation within mitochondria in a manner similar to human cells.

(C) Bacterial and human ribosomes are of different sizes and chemical compositions.

(D) Bacterial cells possess peptidoglycan, whereas human cells do not.

30. Each of the following statements concerning penicillin is correct EXCEPT:

(A) An intact β-lactam ring of penicillin is required for its activity.

(B) The structure of penicillin resembles that of a dipeptide of alanine, which is a component of peptidoglycan.

(C) Penicillin is a bacteriostatic drug because autolytic enzymes are not activated.

(D) Penicillin inhibits transpeptidases, which are required for cross-linking peptidoglycan.

31. Each of the following statements concerning the mechanisms of resistance to antimicrobial drugs is correct EXCEPT:

(A) R factors are plasmids that carry the genes for enzymes that modify one or more drugs.

(B) Resistance to some drugs is due to a chromosomal mutation that alters the receptor for the drug.

(C) Resistance to some drugs is due to transposon genes that code for enzymes that inactivate the drugs.

(D) Resistance genes are rarely transferred by conjugation.

32. Each of the following statements concerning endotoxins is correct EXCEPT:

(A) The toxicity of endotoxins is due to the lipid portion of the molecule.

(B) Endotoxins are found in most gram-positive bacteria.

(C) Endotoxins are located outside of the cell wall peptidoglycan.

(D) The antigenicity of somatic (O) antigen is due to repeating oligosaccharides.

33. Each of the following statements concerning exotoxins is correct EXCEPT:

(A) Exotoxins are polypeptides.

(B) Exotoxins are more easily inactivated by heat than are endotoxins.

(C) Exotoxins are less toxic than the same amount of endotoxins.

(D) Exotoxins can be converted to toxoids.

34. Each of the following statements concerning the killing of bacteria is correct EXCEPT:

(A) A 70% solution of ethanol kills more effectively than absolute (100%) ethanol.

(B) An autoclave uses steam under pressure to reach the killing temperature of 121°C.

(C) The pasteurization of milk kills pathogens but allows many organisms and spores to survive.

(D) Iodine kills by causing the formation of thymine dimers in bacterial DNA.

35. Each of the following statements concerning the drug depicted in the diagram is correct EXCEPT:

image

(A) The drug is bacteriostatic.

(B) The drug inhibits cell wall synthesis.

(C) The drug is made by a fungus.

(D) The portion of the molecule required for activity is labeled B.

36. Each of the following statements concerning the normal flora is correct EXCEPT:

(A) The normal flora of the colon consists predominantly of anaerobic bacteria.

(B) The presence of the normal flora prevents certain pathogens from colonizing the upper respiratory tract.

(C) Fungi (e.g., yeasts) are not members of the normal flora.

(D) Organisms of the normal flora are permanent residents of the body surfaces.

37. Each of the following statements concerning the structure and chemical composition of bacteria is correct EXCEPT:

(A) Some gram-positive cocci contain teichoic acid external to the peptidoglycan.

(B) Some gram-positive rods produce spores that are resistant to boiling.

(C) Some gram-negative rods contain lipid A in their outer cell membrane.

(D) Some mycoplasmas contain pentaglycine in their peptidoglycan.

38. Each of the following statements concerning the normal flora is correct EXCEPT:

(A) Streptococcus mutans is found in the mouth and contributes to the formation of dental caries.

(B) The predominant organisms in the alveoli are viridans streptococci.

(C) Bacteroides fragilis is found in greater numbers than Escherichia coli in the colon.

(D) Candida albicans is part of the normal flora of both men and women.

39. Each of the following statements concerning cholera toxin is correct EXCEPT:

(A) Cholera toxin inhibits elongation factor-2 in the mucosal epithelium.

(B) Binding of cholera toxin to the mucosal epithelium occurs via interaction of the B subunit of the toxin with a ganglioside in the cell membrane.

(C) Cholera toxin acts by adding ADP-ribose to a G protein.

(D) Cholera toxin activates the enzyme adenylate cyclase in the enterocyte.

Answers (Questions 1–39)

1. (D)

2. (C)

3. (A)

4. (D)

5. (C)

6. (B)

7. (C)

8. (B)

9. (D)

10. (B)

11. (C)

12. (D)

13. (C)

14. (B)

15. (D)

16. (D)

17. (D)

18. (C)

19. (A)

20. (C)

21. (D)

22. (B)

23. (A)

24. (B)

25. (A)

26. (D)

27. (C)

28. (D)

29. (B)

30. (C)

31. (D)

32. (B)

33. (C)

34. (D)

35. (A)

36. (C)

37. (D)

38. (B)

39. (A)

DIRECTIONS (Questions 40–51): Select the ONE lettered option that is MOST closely associated with the numbered items. Each lettered option may be selected once, more than once, or not at all.

Questions 40–43

(A) Penicillins

(B) Aminoglycosides

(C) Chloramphenicol

(D) Rifampin

(E) Sulfonamides

40. Inhibit(s) bacterial RNA polymerase

41. Inhibit(s) cross-linking of peptidoglycan

42. Inhibit(s) protein synthesis by binding to the 30S ribosomal subunit

43. Inhibit(s) folic acid synthesis

Questions 44–46

(A) Transduction

(B) Conjugation

(C) DNA transformation

(D) Transposition

44. During an outbreak of gastrointestinal disease caused by an Escherichia coli strain sensitive to ampicillin, tetracycline, and chloramphenicol, a stool sample from one patient yields E. coli with the same serotype resistant to the three antibiotics.

45. A mutant cell line lacking a functional thymidine kinase gene was exposed to a preparation of DNA from normal cells; under appropriate growth conditions, a colony of cells was isolated that makes thymidine kinase.

46. A retrovirus without an oncogene does not induce leukemia in mice; after repeated passages through mice, viruses recovered from a tumor were highly oncogenic and contained a new gene.

Questions 47–51

(A) Diphtheria toxin

(B) Tetanus toxin

(C) Botulinum toxin

(D) Toxic shock syndrome toxin

(E) Cholera toxin

47. Causes paralysis by blocking release of acetylcholine

48. Inhibits protein synthesis by blocking elongation factor-2

49. Stimulates T cells to produce cytokines

50. Stimulates the production of cyclic AMP by adding ADP-ribose to a G protein

51. Inhibits the release of inhibitory neurotransmitters causing muscle spasms

Answers (Questions 40–51)

40. (D)

41. (A)

42. (B)

43. (E)

44. (B)

45. (C)

46. (A)

47. (C)

48. (A)

49. (D)

50. (E)

51. (B)

CLINICAL BACTERIOLOGY

DIRECTIONS (Questions 52–136): Select the ONE lettered answer that is BEST in each question.

52. An outbreak of sepsis caused by Staphylococcus aureus has occurred in the newborn nursery. You are called upon to investigate. According to your knowledge of the normal flora, what is the MOST likely source of the organism?

(A) Colon

(B) Nose

(C) Throat

(D) Vagina

53. Each of the statements about the classification of streptococci is correct EXCEPT:

(A) Pneumococci (Streptococcus pneumoniae) are α-hemolytic and can be serotyped on the basis of their polysaccharide capsules.

(B) Enterococci are group D streptococci and can be classified by their ability to grow in 6.5% sodium chloride.

(C) Although pneumococci and the viridans streptococci are α-hemolytic, they can be differentiated by the bile solubility test and their susceptibility to optochin.

(D) Viridans streptococci are identified by Lancefield grouping, which is based on the C carbohydrate in the cell wall.

54. Each of the following agents is a recognized cause of diarrhea EXCEPT:

(A) Clostridium perfringens

(B) Enterococcus faecalis

(C) Escherichia coli

(D) Vibrio cholerae

55. Each of the following organisms is an important cause of urinary tract infections EXCEPT:

(A) Escherichia coli

(B) Proteus mirabilis

(C) Klebsiella pneumoniae

(D) Bacteroides fragilis

56. Your patient is a 30-year-old woman with nonbloody diarrhea for the past 14 hours. Which one of the following organisms is LEAST likely to cause this illness?

(A) Clostridium difficile

(B) Streptococcus pyogenes

(C) Shigella dysenteriae

(D) Salmonella enteritidis

57. Each of the following statements concerning Mycobacterium tuberculosis is correct EXCEPT:

(A) After being stained with carbolfuchsin, M. tuberculosis resists decolorization with acid alcohol.

(B) M. tuberculosis has a large amount of mycolic acid in its cell wall.

(C) M. tuberculosis appears as a red rod in Gram-stained specimens.

(D) M. tuberculosis appears as a red rod in acid-fast stained specimens.

58. A 50-year-old homeless alcoholic has a fever and is coughing up 1 cup of green, foul-smelling sputum per day. You suspect that he may have a lung abscess. Which one of the following pairs of organisms is MOST likely to be the cause?

(A) Listeria monocytogenes and Legionella pneumophila

(B) Nocardia asteroides and Mycoplasma pneumoniae

(C) Fusobacterium nucleatum and Peptostreptococcus intermedius

(D) Clostridium perfringens and Chlamydia psittaci

59. Which one of the following diseases is BEST diagnosed by serologic means?

(A) Q fever

(B) Pulmonary tuberculosis

(C) Gonorrhea

(D) Actinomycosis

60. Your patient has subacute bacterial endocarditis caused by a member of the viridans group of streptococci. Which one of the following sites is MOST likely to be the source of the organism?

(A) Skin

(B) Colon

(C) Oropharynx

(D) Urethra

61. A culture of skin lesions from a patient with pyoderma (impetigo) shows numerous colonies surrounded by a zone of beta hemolysis on a blood agar plate. A Gram-stained smear shows gram-positive cocci. If you found the catalase test to be negative, which one of the following organisms would you MOST probably have isolated?

(A) Streptococcus pyogenes

(B) Staphylococcus aureus

(C) Staphylococcus epidermidis

(D) Streptococcus pneumoniae

62. The coagulase test, in which the bacteria cause plasma to clot, is used to distinguish:

(A) Streptococcus pyogenes from Enterococcus faecalis

(B) Streptococcus pyogenes from Staphylococcus aureus

(C) Staphylococcus aureus from Staphylococcus epidermidis

(D) Staphylococcus epidermidis from Neisseria meningitidis

63. Which one of the following is a virulence factor for Staphylococcus aureus?

(A) A heat-labile toxin that inhibits glycine release at the internuncial neuron

(B) An oxygen-labile hemolysin

(C) Resistance to novobiocin

(D) Protein A that binds to the Fc portion of IgG

64. Which one of the following host defense mechanisms is the MOST important for preventing dysentery caused by Salmonella?

(A) Gastric acid

(B) Salivary enzymes

(C) Normal flora of the mouth

(D) Alpha interferon

65. The MOST important protective function of the antibody stimulated by tetanus immunization is:

(A) To opsonize the pathogen (Clostridium tetani)

(B) To prevent growth of the pathogen

(C) To prevent adherence of the pathogen

(D) To neutralize the toxin of the pathogen

66. Five hours after eating reheated rice at a restaurant, a 24-year-old woman and her husband both developed nausea, vomiting, and diarrhea. Which one of the following organisms is the MOST likely to be involved?

(A) Clostridium perfringens

(B) Enterotoxigenic Escherichia coli

(C) Bacillus cereus

(D) Salmonella typhi

67. Which one of the following bacteria has the LOWEST 50% infectious dose (ID50)?

(A) Shigella sonnei

(B) Vibrio cholerae

(C) Salmonella typhi

(D) Campylobacter jejuni

68. For which one of the following enteric illnesses is a chronic carrier state MOST likely to develop?

(A) Campylobacter enterocolitis

(B) Shigella enterocolitis

(C) Cholera

(D) Typhoid fever

69. Which one of the following zoonotic illnesses has NO arthropod vector?

(A) Plague

(B) Lyme disease

(C) Brucellosis

(D) Epidemic typhus

70. Which one of the following organisms principally infects vascular endothelial cells?

(A) Salmonella typhi

(B) Rickettsia rickettsii

(C) Haemophilus influenzae

(D) Coxiella burnetii

71. Which one of the following statements MOST accurately depicts the ability of the organism to be cultured in the laboratory?

(A) Treponema pallidum from a chancre can be grown on a special artificial medium supplemented with cholesterol.

(B) Mycobacterium leprae can be grown in the armadillo and the mouse footpad but not on any artificial media.

(C) Mycobacterium tuberculosis can be grown on enriched artificial media and produces visible colonies in 48 to 96 hours.

(D) Atypical mycobacteria are found widely in soil and water but cannot be cultured on artificial media in the laboratory.

72. Each of the following statements concerning chlamydiae is correct EXCEPT:

(A) Chlamydiae are strict intracellular parasites because they cannot synthesize sufficient adenosine triphosphate (ATP).

(B) Chlamydiae possess both DNA and RNA and are bounded by a cell wall.

(C) Chlamydia trachomatis has multiple serotypes that can cause different diseases.

(D) Most chlamydiae are transmitted by arthropods.

73. For which one of the following bacterial vaccines are toxic side effects an important concern?

(A) The vaccine containing pneumococcal polysaccharide

(B) The vaccine containing killed Bordetella pertussis

(C) The vaccine containing tetanus toxoid

(D) The vaccine containing diphtheria toxoid

74. Each of the following statements concerning Staphylococcus aureus is correct EXCEPT:

(A) Gram-positive cocci in grapelike clusters are seen on Gram-stained smear.

(B) The coagulase test is positive.

(C) Treatment should include a β-lactamase–resistant penicillin.

(D) Endotoxin is an important pathogenetic factor.

75. Your patient is a 70-year-old man who underwent bowel surgery for colon cancer 3 days ago. He now has a fever and abdominal pain. You are concerned that he may have peritonitis. Which one of the following pairs of organisms is MOST likely to be the cause?

(A) Bacteroides fragilis and Klebsiella pneumoniae

(B) Bordetella pertussis and Salmonella enteritidis

(C) Actinomyces israelii and Campylobacter jejuni

(D) Clostridium botulinum and Shigella dysenteriae

76. A 65-year-old man develops dysuria and hematuria. A Gram stain of a urine sample shows gram-negative rods. Culture of the urine on EMB agar reveals lactose-negative colonies without evidence of swarming motility. Which one of the following organisms is MOST likely to be the cause of his urinary tract infection?

(A) Enterococcus faecalis

(B) Pseudomonas aeruginosa

(C) Proteus vulgaris

(D) Escherichia coli

77. A 25-year-old man complains of a urethral discharge. You perform a Gram stain on a specimen of the discharge and see neutrophils but no bacteria. Of the organisms listed, the one MOST likely to cause the discharge is:

(A) Treponema pallidum

(B) Chlamydia trachomatis

(C) Candida albicans

(D) Coxiella burnetii

78. Two hours after a delicious Thanksgiving dinner of barley soup, roast turkey, stuffing, sweet potato, green beans, cranberry sauce, and pumpkin pie topped with whipped cream, the Smith family of four experience vomiting and diarrhea. Which one of the following organisms is MOST likely to cause these symptoms?

(A) Shigella flexneri

(B) Campylobacter jejuni

(C) Staphylococcus aureus

(D) Salmonella enteritidis

79. Your patient has a brain abscess that was detected 1 month after a dental extraction. Which one of the following organisms is MOST likely to be involved?

(A) Anaerobic streptococci

(B) Mycobacterium smegmatis

(C) Lactobacillus acidophilus

(D) Mycoplasma pneumoniae

80. The MOST important contribution of the capsule of Streptococcus pneumoniae to virulence is:

(A) To prevent dehydration of the organisms on mucosal surfaces

(B) To retard phagocytosis by polymorphonuclear leukocytes

(C) To inhibit polymorphonuclear leukocyte chemotaxis

(D) To accelerate tissue invasion by its collagenase-like activity

81. The MOST important way the host counteracts the function of the pneumococcal polysaccharide capsule is via:

(A) T lymphocytes sensitized to polysaccharide antigens

(B) Polysaccharide-degrading enzymes

(C) Anticapsular antibody

(D) Activated macrophages

82. The pathogenesis of which one of the following organisms is MOST likely to involve invasion of the intestinal mucosa?

(A) Vibrio cholerae

(B) Shigella sonnei

(C) Enterotoxigenic Escherichia coli

(D) Clostridium botulinum

83. Which one of the following organisms that infects the gastrointestinal tract is the MOST frequent cause of bacteremia?

(A) Shigella flexneri

(B) Campylobacter jejuni

(C) Vibrio cholerae

(D) Salmonella typhi

84. A 30-year-old woman with systemic lupus erythematosus is found to have a positive serologic test for syphilis (VDRL test). She denies having had sexual contact with a partner who had symptoms of a venereal disease. The next best step would be to:

(A) Reassure her that the test is a false-positive reaction related to her autoimmune disorder

(B) Trace her sexual contacts for serologic testing

(C) Treat her with penicillin

(D) Perform a fluorescent treponemal antibody-absorbed (FTA-ABS) test on a specimen of her serum

85. Each of the following statements concerning Treponema is correct EXCEPT:

(A) T. pallidum produces an exotoxin that stimulates adenylate cyclase.

(B) T. pallidum cannot be grown on conventional laboratory media.

(C) Treponemes are members of the normal flora of the human oropharynx.

(D) Patients infected with T. pallidum produce antibodies that react with beef heart cardiolipin.

86. Each of the following statements concerning clostridia is correct EXCEPT:

(A) Pathogenic clostridia are found both in the soil and in the normal flora of the colon.

(B) Antibiotic-associated (pseudomembranous) colitis is due to a toxin produced by Clostridium difficile.

(C) Anaerobic conditions at the wound site are not required to cause tetanus, because spores will form in the presence of oxygen.

(D) Botulism, which is caused by ingesting preformed toxin, can be prevented by boiling food prior to eating.

87. Each of the following statements concerning Bacteroides fragilis is correct EXCEPT:

(A) B. fragilis is a gram-negative rod that is part of the normal flora of the colon.

(B) B. fragilis forms endospores, which allow it to survive in the soil.

(C) The capsule of B. fragilis is an important virulence factor.

(D) B. fragilis infections are characterized by foul-smelling pus.

88. Each of the following statements concerning staphylococci is correct EXCEPT:

(A) S. aureus is differentiated from S. epidermidis by the production of coagulase.

(B) S. aureus infections are often associated with abscess formation.

(C) The majority of clinical isolates of S. aureus produce penicillinase; therefore, penicillin G should not be used for antibiotic therapy for S. aureus infections.

(D) Scalded skin syndrome caused by S. aureus is due to enzymatic degradation of epidermal desmosomes by catalase.

89. Acute glomerulonephritis is a nonsuppurative complication that follows infection by which one of the following organisms?

(A) Enterococcus faecalis

(B) Streptococcus pyogenes

(C) Streptococcus pneumoniae

(D) Streptococcus agalactiae

90. Each of the following statements concerning gram-negative rods is correct EXCEPT:

(A) Escherichia coli is part of the normal flora of the colon; therefore, it does not cause diarrhea.

(B) E. coli ferments lactose, whereas the enteric pathogens Shigella and Salmonella do not.

(C) Klebsiella pneumoniae, although a cause of pneumonia, is part of the normal flora of the colon.

(D) Proteus species are highly motile organisms that are found in the human colon and cause urinary tract infections.

91. A 70-year-old man is found to have a hard mass in his prostate, which is suspected to be a carcinoma. Twenty-four hours after surgical removal of the mass, he develops fever to 39°C and has several shaking chills. Of the organisms listed, which one is LEAST likely to be involved?

(A) Escherichia coli

(B) Enterococcus faecalis

(C) Klebsiella pneumoniae

(D) Legionella pneumophila

92. Five days ago a 65-year-old woman with a lower urinary tract infection began taking ampicillin. She now has a fever and severe diarrhea. Of the organisms listed, which one is MOST likely to be the cause of the diarrhea?

(A) Clostridium difficile

(B) Bacteroides fragilis

(C) Proteus mirabilis

(D) Bordetella pertussis

93. The pathogenesis of which one of the following diseases does NOT involve an exotoxin?

(A) Scarlet fever

(B) Typhoid fever

(C) Toxic shock syndrome

(D) Botulism

94. Regarding the effect of benzylpenicillin (penicillin G) on bacteria, which one of the following organisms is LEAST likely to be resistant?

(A) Staphylococcus aureus

(B) Enterococcus faecalis

(C) Streptococcus pyogenes

(D) Neisseria gonorrhoeae

95. Which one of the following organisms is MOST likely to be the cause of pneumonia in an immunocompetent young adult?

(A) Nocardia asteroides

(B) Serratia marcescens

(C) Mycoplasma pneumoniae

(D) Legionella pneumophila

96. Each of the following statements concerning chlamydial genital tract infections is correct EXCEPT:

(A) Infection can be diagnosed by finding antichlamydial antibody in a serum specimen.

(B) Infection can persist after administration of penicillin.

(C) Symptomatic infections can be associated with urethral or cervical discharge containing many polymorphonuclear leukocytes.

(D) There is no vaccine against these infections.

97. Which one of the following illnesses is NOT a zoonosis?

(A) Typhoid fever

(B) Q fever

(C) Tularemia

(D) Rocky Mountain spotted fever

98. Which one of the following is NOT a characteristic of the Staphylococcus associated with toxic shock syndrome?

(A) Release of a superantigen

(B) Coagulase production

(C) Appearance of the organism in grapelike clusters on Gram-stained smear

(D) Catalase-negative reaction

99. Which one of the following is NOT an important characteristic of either Neisseria gonorrhoeae or Neisseria meningitidis?

(A) Polysaccharide capsule

(B) IgA protease

(C) M protein

(D) Pili

100. Which one of the following is NOT an important characteristic of Streptococcus pyogenes?

(A) Protein A

(B) M protein

(C) Beta-hemolysin

(D) Polysaccharide group-specific substance

101. Each of the following is associated with the Lancefield group B streptococci (S. agalactiae) EXCEPT:

(A) Pyoderma (impetigo)

(B) Vaginal carriage in 5% to 25% of normal women of childbearing age

(C) Neonatal sepsis and meningitis

(D) Beta-hemolysis

102. Three organisms, Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae, cause the vast majority of cases of bacterial meningitis. What is the MOST important pathogenic component they share?

(A) Protein A

(B) Capsule

(C) Endotoxin

(D) β-Lactamase

103. Diarrhea caused by which one of the following agents is characterized by the presence of fecal leukocytes?

(A) Campylobacter jejuni

(B) Rotavirus

(C) Clostridium perfringens

(D) Enterotoxigenic Escherichia coli

104. Each of the following statements concerning Chlamydia trachomatis is correct EXCEPT:

(A) It is an important cause of nongonococcal urethritis.

(B) It is the cause of lymphogranuloma venereum.

(C) It is an important cause of subacute bacterial endocarditis.

(D) It is an important cause of conjunctivitis.

105. Each of the following statements concerning Actinomyces and Nocardia is correct EXCEPT:

(A) A. israelii is an anaerobic rod found as part of the normal flora in the mouth.

(B) Both Actinomyces and Nocardia are branching, filamentous rods.

(C) N. asteroides causes infections primarily in immunocompromised patients.

(D) Infections are usually diagnosed by detecting a significant rise in antibody titer.

106. Which one of the following types of organisms is NOT an obligate intracellular parasite and therefore can replicate on bacteriologic media?

(A) Chlamydia

(B) Mycoplasma

(C) Adenovirus

(D) Rickettsia

107. Tissue-degrading enzymes play an important role in the pathogenesis of several bacteria. Which one of the following is NOT involved in tissue or cell damage?

(A) Lecithinase of Clostridium perfringens

(B) Hyaluronidase of Streptococcus pyogenes

(C) M protein of Streptococcus pneumoniae

(D) Leukocidin of Staphylococcus aureus

108. The soil is the natural habitat for certain microorganisms of medical importance. Which one of the following is LEAST likely to reside there?

(A) Clostridium tetani

(B) Mycobacterium avium-intracellulare

(C) Bacillus anthracis

(D) Chlamydia trachomatis

109. Which one of the following organisms is the MOST frequent bacterial cause of pharyngitis?

(A) Staphylococcus aureus

(B) Streptococcus pneumoniae

(C) Streptococcus pyogenes

(D) Neisseria meningitidis

110. Several pathogens are transmitted either during gestation or at birth. Which one of the following is LEAST likely to be transmitted at these times?

(A) Haemophilus influenzae

(B) Treponema pallidum

(C) Neisseria gonorrhoeae

(D) Chlamydia trachomatis

111. Each of the following statements concerning exotoxins is correct EXCEPT:

(A) Some strains of Escherichia coli produce an enterotoxin that causes diarrhea.

(B) Cholera toxin acts by stimulating adenylate cyclase.

(C) Diphtheria is caused by an exotoxin that inhibits protein synthesis by inactivating an elongation factor.

(D) Botulism is caused by a toxin that hydrolyzes lecithin (lecithinase), thereby destroying nerve cells.

112. Each of the following statements concerning the VDRL test for syphilis is correct EXCEPT:

(A) The antigen is composed of inactivated Treponema pallidum.

(B) The test is usually positive in secondary syphilis.

(C) False-positive results are more frequent than with the fluorescent treponemal antibody-absorbed (FTA-ABS) test.

(D) The antibody titer declines with appropriate therapy.

113. Each of the following statements concerning the fluorescent treponemal antibody-absorbed (FTA-ABS) test for syphilis is correct EXCEPT:

(A) The test is specific for Treponema pallidum.

(B) The patient’s serum is absorbed with saprophytic treponemes.

(C) Once positive, the test remains so despite appropriate therapy.

(D) The test is rarely positive in primary syphilis.

114. Each of the following statements concerning Corynebacterium diphtheriae is correct EXCEPT:

(A) C. diphtheriae is a gram-positive rod that does not form spores.

(B) Toxin production is dependent on the organism’s being lysogenized by a bacteriophage.

(C) Diphtheria toxoid should not be given to children younger than 3 years because the incidence of complications is too high.

(D) Antitoxin should be used to treat patients with diphtheria.

115. Each of the following statements concerning certain gram-negative rods is correct EXCEPT:

(A) Pseudomonas aeruginosa causes wound infections that are characterized by blue-green pus as a result of pyocyanin production.

(B) In unimmunized individuals, invasive disease caused by Haemophilus influenzae is most often due to strains possessing a type b polysaccharide capsule.

(C) Legionella pneumophila infection is acquired by inhalation of aerosols from environmental water sources.

(D) Whooping cough, which is caused by Bordetella pertussis, is on the rise because changing antigenicity of the organism has made the vaccine relatively ineffective.

116. Each of the following statements concerning enterotoxins is correct EXCEPT:

(A) Enterotoxins typically cause bloody diarrhea with leukocytes in the stool.

(B) Staphylococcus aureus produces an enterotoxin that causes vomiting and diarrhea.

(C) Vibrio cholerae causes cholera by producing an enterotoxin that increases adenylate cyclase activity within the enterocyte.

(D) Escherichia coli enterotoxin mediates ADP-ribosylation of a G protein.

117. Each of the following statements concerning plague is correct EXCEPT:

(A) Plague is caused by a gram-negative rod that can be cultured on blood agar.

(B) Plague is transmitted from the animal reservoir to humans by flea bite.

(C) The main reservoirs in nature are small rodents.

(D) Plague is of concern in many underdeveloped countries but has not occurred in the United States since 1968.

118. Which one of the following statements concerning the organisms that cause brucellosis is CORRECT?

(A) Brucellae are transmitted primarily by tick bite.

(B) The principal reservoirs of Brucellae are small rodents.

(C) Brucellae infect reticuloendothelial cells in the liver, spleen, and bone marrow.

(D) Brucellae are obligate intracellular parasites that are usually identified by growth in human cell culture.

119. Each of the following statements concerning epidemic typhus is correct EXCEPT:

(A) The disease is characterized by a rash.

(B) The Weil-Felix test can aid in diagnosis of the disease.

(C) The disease is caused by a Rickettsia.

(D) The causative organism is transmitted from rodents to humans by a tick.

120. Which one of the following organisms causes diarrhea by producing an enterotoxin that increases adenylate cyclase activity within enterocytes?

(A) Escherichia coli

(B) Bacteroides fragilis

(C) Staphylococcus aureus

(D) Enterococcus faecalis

121. Each of the following statements concerning Rocky Mountain spotted fever is correct EXCEPT:

(A) The causative organism forms beta-hemolytic colonies on blood agar.

(B) Headache, fever, and rash are characteristic features of the disease.

(C) The disease occurs primarily east of the Mississippi.

(D) The disease is caused by a Rickettsia.

122. Each of the following statements concerning Clostridium perfringens is correct EXCEPT:

(A) It causes gas gangrene.

(B) It causes food poisoning.

(C) It produces an exotoxin that degrades lecithin and causes necrosis and hemolysis.

(D) It is a gram-negative rod that does not ferment lactose.

123. Each of the following statements concerning Clostridium tetani is correct EXCEPT:

(A) It is a gram-positive, spore-forming rod.

(B) Pathogenesis is due to the production of an exotoxin that blocks inhibitory neurotransmitters.

(C) It is a facultative organism; it will grow on a blood agar plate in the presence of room air.

(D) Its natural habitat is primarily the soil.

124. Each of the following statements concerning spirochetes is correct EXCEPT:

(A) Species of Treponema are part of the normal flora of the mouth.

(B) Species of Borrelia cause a tick-borne disease called relapsing fever.

(C) The species of Leptospira that cause leptospirosis grow primarily in humans and are usually transmitted by human-to-human contact.

(D) Species of Treponema cause syphilis and yaws.

125. Each of the following statements concerning gonorrhea is correct EXCEPT:

(A) Infection in men is more frequently symptomatic than in women.

(B) A presumptive diagnosis can be made by finding gram-negative kidney bean-shaped diplococci within neutrophils in a urethral discharge.

(C) The definitive diagnosis can be made by detecting antibodies to Neisseria gonorrhoeae in the patient’s serum.

(D) Gonococcal conjunctivitis of the newborn rarely occurs in the United States, because silver nitrate or erythromycin is commonly used as prophylaxis.

126. Each of the following statements concerning Mycobacterium tuberculosis is correct EXCEPT:

(A) Some strains of M. tuberculosis isolated from patients exhibit multiple drug resistance (i.e., they are resistant to both isoniazid and rifampin).

(B) M. tuberculosis contains a small amount of lipid in its cell wall and therefore stains poorly with the Gram stain.

(C) M. tuberculosis grows slowly, often requiring 3 to 6 weeks before colonies appear.

(D) The antigen in the tuberculin skin test is a protein extracted from the organism.

127. Which one of the following statements concerning immunization against diseases caused by clostridia is CORRECT?

(A) Antitoxin against tetanus protects against botulism as well, because the two toxins share antigenic sites.

(B) Vaccines containing alpha toxin (lecithinase) are effective in protecting against gas gangrene.

(C) The toxoid vaccine against Clostridium difficile infection should be administered to immunocompromised patients.

(D) Immunization with tetanus toxoid induces effective protection against tetanus toxin.

128. Each of the following statements concerning neisseriae is correct EXCEPT:

(A) They are gram-negative diplococci.

(B) They produce IgA protease as a virulence factor.

(C) They are oxidase-positive.

(D) They grow best under anaerobic conditions.

129. Which one of the following statements concerning Legionella pneumophila is CORRECT?

(A) It is part of the normal flora of the colon.

(B) It cannot be grown on laboratory media.

(C) It does not have a cell wall.

(D) It causes atypical pneumonia, especially in those with reduced cell-mediated immunity.

130. Each of the following statements concerning wound infections caused by Clostridium perfringens is correct EXCEPT:

(A) An exotoxin plays a role in pathogenesis.

(B) Gram-positive rods are found in the exudate.

(C) The organism grows only in human cell culture.

(D) Anaerobic culture of the wound site should be ordered.

131. Each of the following statements concerning infection with Chlamydia psittaci is correct EXCEPT:

(A) C. psittaci can be isolated by growth in cell culture and will not grow in blood agar.

(B) The organism appears purple in Gram-stained smears of sputum.

(C) The infection is more readily diagnosed by serologic tests than by isolation of the organism.

(D) The infection is more commonly acquired from a nonhuman source than from another human.

132. Ticks are vectors for the transmission of each of the following diseases EXCEPT:

(A) Rocky Mountain spotted fever

(B) Epidemic typhus

(C) Tularemia

(D) Lyme disease

133. Each of the following statements concerning pneumonia caused by Mycoplasma pneumoniae is correct EXCEPT:

(A) Pneumonia caused by M. pneumoniae is associated with a rise in the titer of cold agglutinins.

(B) Pneumonia caused by M. pneumoniae occurs primarily in immunocompetent individuals.

(C) Pneumonia caused by M. pneumoniae is an “atypical” pneumonia.

(D) M. pneumoniae cannot be cultured in vitro because it has no cell wall.

134. Each of the following statements concerning Neisseria meningitidis is correct EXCEPT:

(A) It is an oxidase-positive, gram-negative diplococcus.

(B) It contains endotoxin in its cell wall.

(C) It produces an exotoxin that stimulates adenylate cyclase.

(D) It has a polysaccharide capsule that is antiphagocytic.

135. Each of the following statements concerning Q fever is correct EXCEPT:

(A) Rash is a prominent feature.

(B) It is transmitted by respiratory aerosol.

(C) Farm animals are an important reservoir.

(D) It is caused by Coxiella burnetii.

136. Each of the following statements concerning Mycobacterium leprae is correct EXCEPT:

(A) In lepromatous leprosy, large numbers of organisms are usually seen in acid-fast-stained smears.

(B) The organism will grow on bacteriologic media in 3 to 6 weeks.

(C) Prolonged therapy (9 months or longer) is required to prevent recurrence.

(D) Loss of sensation due to nerve damage is often seen in leprosy.

Answers (Questions 52–136)

52. (B)

53. (D)

54. (B)

55. (D)

56. (B)

57. (C)

58. (C)

59. (A)

60. (C)

61. (A)

62. (C)

63. (D)

64. (A)

65. (D)

66. (C)

67. (A)

68. (D)

69. (C)

70. (B)

71. (B)

72. (D)

73. (B)

74. (D)

75. (A)

76. (B)

77. (B)

78. (C)

79. (A)

80. (B)

81. (C)

82. (B)

83. (D)

84. (D)

85. (A)

86. (C)

87. (B)

88. (D)

89. (B)

90. (A)

91. (D)

92. (A)

93. (B)

94. (C)

95. (C)

96. (A)

97. (A)

98. (D)

99. (C)

100. (A)

101. (A)

102. (B)

103. (A)

104. (C)

105. (D)

106. (B)

107. (C)

108. (D)

109. (C)

110. (A)

111. (D)

112. (A)

113. (D)

114. (C)

115. (D)

116. (A)

117. (D)

118. (C)

119. (D)

120. (A)

121. (A)

122. (D)

123. (C)

124. (C)

125. (C)

126. (B)

127. (D)

128. (D)

129. (D)

130. (C)

131. (B)

132. (B)

133. (D)

134. (C)

135. (A)

136. (B)

DIRECTIONS (Questions 137–158): Select the ONE lettered option that is MOST closely associated with the numbered items. Each lettered option may be selected once, more than once, or not at all.

Questions 137–140

(A) Mycobacterium avium-intracellulare

(B) Treponema pallidum

(C) Rickettsia prowazekii

(D) Mycoplasma pneumoniae

137. Is an obligate intracellular parasite

138. Is found primarily in the soil

139. Has no cell wall

140. Is an acid-fast rod

Questions 141–143

(A) Borrelia burgdorferi

(B) Helicobacter pylori

(C) Pasteurella multocida

(D) Brucella melitensis

141. Peptic ulcer in a 45-year-old salesman

142. Cellulitis of the hand following a cat bite

143. Expanding, bull’s eye–shaped red rash in a 6-year-old boy after a camping trip

Questions 144–147

(A) Corynebacterium diphtheriae

(B) Listeria monocytogenes

(C) Bacillus anthracis

(D) Clostridium botulinum

144. Causes both skin lesions and a severe pneumonia

145. Causes flaccid paralysis

146. Causes a pseudomembrane in the throat, which can cause respiratory tract obstruction

147. Causes meningitis in neonates and the immunosuppressed

Questions 148–150

(A) Escherichia coli

(B) Klebsiella pneumoniae

(C) Salmonella enteritidis

(D) Proteus mirabilis

148. Is frequently implicated in nosocomial infections, is an important cause of community-acquired pneumonia in adults, and has a thick, mucoid capsule

149. Is the most common cause of urinary tract infections

150. Pathogenicity associated primarily with urinary tract infections; produces urease

Questions 151–154

(A) Staphylococcus aureus

(B) Streptococcus pyogenes

(C) Enterococcus faecalis

(D) Streptococcus pneumoniae

151. Grows in 6.5% sodium chloride

152. Is bile soluble

153. Produces enterotoxin

154. Is associated with rheumatic fever

Questions 155–158

(A) Bacteroides fragilis

(B) Haemophilus influenzae

(C) Pseudomonas aeruginosa

(D) Chlamydia pneumoniae

155. Coccobacillary gram-negative rod that causes meningitis in young children

156. Oxidase-positive gram-negative rod that is an important cause of wound and burn infections

157. Causes atypical pneumonia in immunocompetent adults

158. Anaerobic gram-negative rod that is an important cause of peritonitis

Answers (Questions 137–158)

137. (C)

138. (A)

139. (D)

140. (A)

141. (B)

142. (C)

143. (A)

144. (C)

145. (D)

146. (A)

147. (B)

148. (B)

149. (A)

150. (D)

151. (C)

152. (D)

153. (A)

154. (B)

155. (B)

156. (C)

157. (D)

158. (A)

BASIC VIROLOGY

DIRECTIONS (Questions 159–192): Select the ONE lettered answer that is BEST in each question.

159. Viruses enter cells by adsorbing to specific sites on the outer membrane of cells. Each of the following statements regarding this event is correct EXCEPT:

(A) The interaction determines the specific target organs for infection.

(B) The interaction determines whether the purified genome of a virus is infectious.

(C) The interaction can be prevented by neutralizing antibody.

(D) If the sites are occupied, interference with virus infection occurs.

160. Many viruses mature by budding through the outer membrane of the host cell. Each of the following statements regarding these viruses is correct EXCEPT:

(A) Some of these viruses cause multinucleated giant cell formation.

(B) Some new viral antigens appear on the surface of the host cell.

(C) Some of these viruses contain host cell lipids.

(D) Some of these viruses do not have an envelope.

161. Biochemical analysis of a virus reveals the genome to be composed of eight unequally sized pieces of single-stranded RNA, each of which is complementary to viral mRNA in infected cells. Which one of the following statements is UNLIKELY to be correct?

(A) Different proteins are encoded by each segment of the viral genome.

(B) The virus particle contains a virus-encoded enzyme that can copy the genome into its complement.

(C) Purified RNA extracted from the virus particle is infectious.

(D) The virus can acquire new antigens via reassortment of its RNA segments.

162. Latency is an outcome particularly characteristic of which one of the following virus groups?

(A) Polioviruses

(B) Herpesviruses

(C) Rhinoviruses

(D) Influenza viruses

163. Each of the following statements concerning viral serotypes is correct EXCEPT:

(A) In naked nucleocapsid viruses, the serotype is usually determined by the outer capsid proteins.

(B) In enveloped viruses, the serotype is usually determined by the outer envelope proteins, especially the spike proteins.

(C) Some viruses have multiple serotypes.

(D) Some viruses have an RNA polymerase that determines the serotype.

164. The ability of a virus to produce disease can result from a variety of mechanisms. Which one of the following mechanisms is LEAST likely?

(A) Cytopathic effect in infected cells

(B) Malignant transformation of infected cells

(C) Immune response to virus-induced antigens on the surface of infected cells

(D) Production of an exotoxin that activates adenylate cyclase

165. Which one of the following forms of immunity to viruses would be LEAST likely to be lifelong?

(A) Passive immunity

(B) Passive–active immunity

(C) Active immunity

(D) Cell-mediated immunity

166. Which one of the following statements concerning alpha, beta, and gamma interferons is LEAST accurate?

(A) Interferons inhibit a broad range of viruses, not just the virus that induced the interferon.

(B) Interferons are synthesized only by virus-infected cells.

(C) Interferons induce the synthesis of a protein kinase that phosphorylates an elongation factor, thereby inactivating protein synthesis.

(D) Interferons induce the synthesis of a ribonuclease that degrades viral mRNA.

167. You have isolated a virus from the stool of a patient with diarrhea and shown that its genome is composed of multiple pieces of double-stranded RNA. Which one of the following is LEAST LIKELY to be true?

(A) Each piece of RNA encodes a different protein.

(B) The virus encodes an RNA-directed RNA polymerase.

(C) The virion contains an RNA polymerase.

(D) The genome integrates into the host chromosome.

168. A temperate bacteriophage has been induced from a new pathogenic strain of Escherichia coli that produces a toxin. Which one of the following is the MOST convincing way to show that the phage encodes the toxin?

(A) Carry out conjugation of the pathogenic strain with a nonpathogenic strain.

(B) Infect an experimental animal with the phage.

(C) Lysogenize a nonpathogenic strain with the phage.

(D) Look for transposable elements in the phage DNA.

169. Each of the following statements concerning retroviruses is correct EXCEPT:

(A) The virion carries an RNA-directed DNA polymerase encoded by the viral genome.

(B) The viral genome consists of three segments of double-stranded RNA.

(C) The virion is enveloped and enters cells via an interaction with specific receptors on the host cell.

(D) During infection, the virus synthesizes a DNA copy of its RNA, and this DNA becomes covalently integrated into host cell DNA.

170. A stock of virus particles has been found by electron microscopy to contain 108 particles/mL, but a plaque assay reveals only 105 plaque-forming units/mL. The BEST interpretation of these results is that:

(A) Only one particle in 1000 is infectious.

(B) A nonpermissive cell line was used for the plaque assay.

(C) Several kinds of viruses were present in the stock.

(D) The virus is a temperature-sensitive mutant.

171. Reasonable mechanisms for viral persistence in infected individuals include all of the following EXCEPT:

(A) Generation of defective-interfering particles

(B) Virus-mediated inhibition of host DNA synthesis

(C) Integration of a provirus into the genome of the host

(D) Host tolerance to viral antigens

172. Each of the following statements concerning viral surface proteins is correct EXCEPT:

(A) They elicit antibody that neutralizes infectivity of the virus.

(B) They determine the species specificity of the virus–cell interaction.

(C) They participate in active transport of nutrients across the viral envelope membrane.

(D) They protect the genetic material against nucleases.

173. Each of the following statements concerning viral vaccines is correct EXCEPT:

(A) In live, attenuated vaccines, the virus has lost its ability to cause disease but has retained its ability to induce neutralizing antibody.

(B) In live, attenuated vaccines, the possibility of reversion to virulence is of concern.

(C) With inactivated vaccines, IgA mucosal immunity is usually induced.

(D) With inactivated vaccines, protective immunity is due mainly to the production of IgG.

174. The major barrier to the control of rhinovirus upper respiratory infections by immunization is:

(A) The poor local and systemic immune response to these viruses

(B) The large number of serotypes of the rhinoviruses

(C) The side effects of the vaccine

(D) The inability to grow the viruses in cell culture

175. The feature of the influenza virus genome that contributes MOST to the antigenic variation of the virus is:

(A) A high G + C content, which augments binding to nucleoproteins

(B) Inverted repeat regions, which create “sticky ends”

(C) Segmented nucleic acid

(D) Unique methylated bases

176. Which one of the following is the BEST explanation for the selective action of acyclovir (acycloguanosine) in herpes simplex virus (HSV)-infected cells?

(A) Acyclovir binds specifically to viral receptors only on the surface of the HSV-infected cell.

(B) Acyclovir is phosphorylated by a virus-encoded phosphokinase only within HSV-infected cells.

(C) Acyclovir selectively inhibits the RNA polymerase in the HSV virion.

(D) Acyclovir specifically blocks the matrix protein of HSV, thereby preventing release of progeny HSV.

177. Each of the following statements concerning interferon is correct EXCEPT:

(A) Interferon inhibits the growth of both DNA and RNA viruses.

(B) Interferon is induced by double-stranded RNA.

(C) Interferon made by cells of one species acts more effectively in the cells of that species than in the cells of other species.

(D) Interferon acts by preventing viruses from entering the cell.

178. Each of the following statements concerning the viruses that infect humans is correct EXCEPT:

(A) Only viruses with a negative polarity RNA genome have a polymerase in the virion.

(B) The purified nucleic acid of some viruses is infectious, but at a lower efficiency than the intact virions.

(C) Some viruses contain lipoprotein envelopes derived from the plasma membrane of the host cell.

(D) The nucleic acid of some viruses is single-stranded DNA and that of others is double-stranded RNA.

179. Which one of the following statements about virion structure and assembly is CORRECT?

(A) Most viruses acquire surface glycoproteins by budding through the nuclear membrane.

(B) Helical nucleocapsids are found primarily in DNA viruses.

(C) The symmetry of virus particles prevents inclusion of any nonstructural proteins, such as enzymes.

(D) Enveloped viruses use a matrix protein to mediate interactions between viral glycoproteins in the plasma membrane and structural proteins in the nucleocapsid.

180. Each of the following statements concerning viruses is correct EXCEPT:

(A) Viruses can reproduce only within cells.

(B) The proteins on the surface of the virus mediate the entry of the virus into host cells.

(C) Neutralizing antibody is directed against proteins on the surface of the virus.

(D) Viruses replicate by binary fission.

181. Viruses are obligate intracellular parasites. Each of the following statements concerning this fact is correct EXCEPT:

(A) Viruses cannot generate energy outside of cells.

(B) Viruses cannot synthesize proteins outside of cells.

(C) Viruses must degrade host cell DNA in order to obtain nucleotides.

(D) Enveloped viruses require host cell membranes to obtain their envelopes.

182. Each of the following statements concerning lysogeny is correct EXCEPT:

(A) Viral genes replicate independently of bacterial genes.

(B) Viral genes responsible for lysis are repressed.

(C) Viral DNA is integrated into bacterial DNA.

(D) Some lysogenic bacteriophages encode toxins that cause human disease.

183. Each of the following viruses possesses an outer envelope of lipoprotein EXCEPT:

(A) Varicella-zoster virus

(B) Papillomavirus

(C) Influenza virus

(D) Human immunodeficiency virus

184. Which one of the following viruses possesses a genome of single-stranded RNA that is infectious when purified?

(A) Influenza virus

(B) Rotavirus

(C) Measles virus

(D) Poliovirus

185. Each of the following viruses possesses an RNA polymerase in the virion EXCEPT:

(A) Hepatitis A virus

(B) Smallpox virus

(C) Mumps virus

(D) Rotavirus

186. Each of the following viruses possesses a DNA polymerase in the virion EXCEPT:

(A) Human immunodeficiency virus

(B) Human T-cell lymphotropic virus

(C) Epstein–Barr virus

(D) Hepatitis B virus

187. Each of the following viruses possesses double-stranded nucleic acid as its genome EXCEPT:

(A) Coxsackie virus

(B) Herpes simplex virus

(C) Rotavirus

(D) Adenovirus

188. Regarding viroids, which one of the following statements is the MOST accurate?

(A) They are defective viruses that are missing the DNA coding for the matrix protein.

(B) They consist of RNA without a protein or lipoprotein outer coat.

(C) They cause tumors in experimental animals.

(D) They require an RNA polymerase in the particle for replication to occur.

189. Each of the following statements about both measles virus and rubella virus is correct EXCEPT:

(A) They are RNA enveloped viruses.

(B) Their virions contain an RNA polymerase.

(C) They have a single antigenic type.

(D) They are transmitted by respiratory aerosol.

190. Each of the following statements about both influenza virus and rabies virus is correct EXCEPT:

(A) They are enveloped RNA viruses.

(B) Their virions contain an RNA polymerase.

(C) A killed vaccine is available for both viruses.

(D) They each have a single antigenic type.

191. Each of the following statements about both poliovirus and rhinoviruses is correct EXCEPT:

(A) They are nonenveloped RNA viruses.

(B) They have multiple antigenic types.

(C) Their virions contain an RNA polymerase.

(D) They do not integrate their genome into host cell DNA.

192. Each of the following statements about human immunodeficiency virus (HIV) is correct EXCEPT:

(A) HIV is an enveloped RNA virus.

(B) The virion contains an RNA-dependent DNA polymerase.

(C) A DNA copy of the HIV genome integrates into host cell DNA.

(D) Acyclovir inhibits HIV replication.

Answers (Questions 159–192)

159. (B)

160. (D)

161. (C)

162. (B)

163. (D)

164. (D)

165. (A)

166. (B)

167. (D)

168. (C)

169. (B)

170. (A)

171. (B)

172. (C)

173. (C)

174. (B)

175. (C)

176. (B)

177. (D)

178. (A)

179. (D)

180. (D)

181. (C)

182. (A)

183. (B)

184. (D)

185. (A)

186. (C)

187. (A)

188. (B)

189. (B)

190. (D)

191. (C)

192. (D)

DIRECTIONS (Questions 193–211): Select the one lettered option that is MOST CLOSELY associated with the numbered items. Each lettered option may be selected once, more than once, or not at all.

Questions 193–196

(A) DNA enveloped virus

(B) DNA nonenveloped virus

(C) RNA enveloped virus

(D) RNA nonenveloped virus

193. Herpes simplex virus

194. Human T-cell lymphotropic virus

195. Human papillomavirus

196. Rotavirus

Questions 197–201

(A) Attachment and penetration of virion

(B) Viral mRNA synthesis

(C) Viral protein synthesis

(D) Viral genome DNA synthesis

(E) Assembly and release of progeny virus

197. Main site of action of acyclovir

198. Main site of action of amantadine

199. Function of virion polymerase of influenza virus

200. Main site of action of antiviral antibody

201. Step at which budding occurs

Questions 202–206

(A) Poliovirus

(B) Epstein–Barr virus

(C) Prions

(D) Hepatitis B virus

(E) Respiratory syncytial virus

202. Part of the genome DNA is synthesized by the virion polymerase.

203. The translation product of viral mRNA is a polyprotein that is cleaved to form virion structural proteins.

204. It is remarkably resistant to ultraviolet light.

205. It causes latent infection of B cells.

206. An envelope protein induces the formation of giant cells.

Questions 207–211

(A) Hepatitis A virus

(B) Hepatitis B virus

(C) Hepatitis C virus

(D) Hepatitis D virus

207. Enveloped DNA virus that is transmitted by blood

208. Enveloped RNA virus that has the surface antigen of another virus

209. Enveloped RNA virus that is the most common cause of non-A, non-B hepatitis

210. Nonenveloped RNA virus that is transmitted by the fecal–oral route

211. Purified surface protein of this virus is the immunogen in a vaccine.

Answers (Questions 193–211)

193. (A)

194. (C)

195. (B)

196. (D)

197. (D)

198. (A)

199. (B)

200. (A)

201. (E)

202. (D)

203. (A)

204. (C)

205. (B)

206. (E)

207. (B)

208. (D)

209. (C)

210. (A)

211. (B)

CLINICAL VIROLOGY

DIRECTIONS (Questions 212–275): Select the ONE lettered answer that is BEST in each question.

212. Which one of the following outcomes is MOST common following a primary herpes simplex virus infection?

(A) Complete eradication of virus and virus-infected cells

(B) Persistent asymptomatic viremia

(C) Establishment of latent infection

(D) Persistent cytopathic effect in infected cells

213. Each of the following pathogens is likely to establish chronic or latent infection EXCEPT:

(A) Cytomegalovirus

(B) Hepatitis A virus

(C) Hepatitis B virus

(D) Herpes simplex virus

214. Each of the following statements regarding poliovirus and its vaccine is correct EXCEPT:

(A) Poliovirus is transmitted by the fecal–oral route.

(B) Pathogenesis by poliovirus primarily involves the death of sensory neurons.

(C) The live, attenuated vaccine contains all three serotypes of poliovirus.

(D) An unimmunized adult traveling to countries where there is a known risk of being infected with poliovirus should receive the inactivated vaccine.

215. Which one of the following strategies is MOST likely to induce lasting intestinal mucosal immunity to poliovirus?

(A) Parenteral (intramuscular) immunization with inactivated vaccine

(B) Oral administration of poliovirus immune globulin

(C) Parenteral immunization with live vaccine

(D) Oral immunization with live vaccine

216. Each of the following clinical syndromes is associated with infection by picornaviruses EXCEPT:

(A) Myocarditis/pericarditis

(B) Hepatitis

(C) Mononucleosis

(D) Meningitis

217. Each of the following statements concerning rubella vaccine is correct EXCEPT:

(A) The vaccine prevents reinfection, thereby limiting the spread of virulent virus.

(B) The immunogen in the vaccine is killed rubella virus.

(C) The vaccine induces antibodies that prevent dissemination of the virus by neutralizing it during the viremic stage.

(D) The incidence of both childhood rubella and congenital rubella syndrome has decreased significantly since the advent of the vaccine.

218. Each of the following statements concerning the rabies vaccine for use in humans is correct EXCEPT:

(A) The vaccine contains live, attenuated rabies virus.

(B) If your patient is bitten by a wild animal (e.g., a skunk) the rabies vaccine should be given.

(C) When the vaccine is used for postexposure prophylaxis, rabies immune globulin should also be given.

(D) The virus in the vaccine is grown in human cell cultures, thus decreasing the risk of allergic encephalomyelitis.

219. Each of the following statements concerning influenza is correct EXCEPT:

(A) Major epidemics of the disease are caused by influenza A viruses rather than influenza B and C viruses.

(B) Likely sources of new antigens for influenza A viruses are the viruses that cause influenza in animals.

(C) Major antigenic changes (shifts) of viral surface proteins are seen primarily in influenza A viruses rather than in influenza B and C viruses.

(D) The antigenic changes that occur with antigenic drift are due to reassortment of the multiple pieces of the influenza virus genome.

220. Each of the following statements concerning the prevention and treatment of influenza is correct EXCEPT:

(A) The inactivated influenza vaccine contains H1N1 virus, whereas the live, attenuated influenza vaccine contains H3N2 virus.

(B) The vaccine is recommended to be given each year because the antigenicity of the virus drifts.

(C) Oseltamivir (Tamiflu) is effective against both influenza A and influenza B viruses.

(D) The main antigen in the vaccine that induces protective antibody is the hemagglutinin.

221. A 6-month-old child develops a persistent cough and a fever. Physical examination and chest X-ray suggest pneumonia. Which one of the following organisms is LEAST likely to cause this infection?

(A) Respiratory syncytial virus

(B) Adenovirus

(C) Parainfluenza virus

(D) Rotavirus

222. A 45-year-old man was attacked by a bobcat and bitten repeatedly about the face and neck. The animal was shot by a companion and brought back to the public health authorities. Once you decide to immunize against rabies virus, how would you proceed?

(A) Use hyperimmune serum only

(B) Use active immunization only

(C) Use hyperimmune serum and active immunization

(D) Use active immunization and follow this with hyperimmune serum if adequate antibody titers are not obtained in the patient’s serum

223. Each of the following statements concerning mumps is correct EXCEPT:

(A) Mumps virus is a paramyxovirus and hence has a single-stranded RNA genome.

(B) Meningitis is a recognized complication of mumps.

(C) Mumps orchitis in children prior to puberty often causes sterility.

(D) During mumps, the virus spreads through the bloodstream (viremia) to various internal organs.

224. Each of the following statements concerning respiratory syncytial virus (RSV) is correct EXCEPT:

(A) RSV has a single-stranded RNA genome.

(B) RSV induces the formation of multinucleated giant cells.

(C) RSV causes pneumonia primarily in children.

(D) RSV infections can be effectively treated with acyclovir.

225. The principal reservoir for the antigenic shift variants of influenza virus appears to be:

(A) People in isolated communities such as the Arctic

(B) Animals, specifically pigs, horses, and fowl

(C) Soil, especially in the tropics

(D) Sewage

226. The role of an infectious agent in the pathogenesis of kuru was BEST demonstrated by which one of the following observations?

(A) A 16-fold rise in antibody titer to the agent was observed.

(B) The viral genome was isolated from infected neurons.

(C) Electron micrographs of the brains of infected individuals demonstrated intracellular structures resembling paramyxovirus nucleocapsids.

(D) The disease was serially transmitted to experimental animals.

227. A 64-year-old man with chronic lymphatic leukemia develops progressive deterioration of mental and neuromuscular function. At autopsy the brain shows enlarged oligodendrocytes whose nuclei contain naked, icosahedral virus particles. The MOST likely diagnosis is:

(A) Herpes encephalitis

(B) Creutzfeldt-Jakob disease

(C) Subacute sclerosing panencephalitis

(D) Progressive multifocal leukoencephalopathy

(E) Rabies

228. A 20-year-old man, who for many years had received daily injections of growth hormone prepared from human pituitary glands, develops ataxia, slurred speech, and dementia. At autopsy the brain shows widespread neuronal degeneration, a spongy appearance due to many vacuoles between the cells, no inflammation, and no evidence of virus particles. The MOST likely diagnosis is:

(A) Herpes encephalitis

(B) Creutzfeldt-Jakob disease

(C) Subacute sclerosing panencephalitis

(D) Progressive multifocal leukoencephalopathy

(E) Rabies

229. A 24-year-old woman has had fever and a sore throat for the past week. Moderately severe pharyngitis and bilateral cervical lymphadenopathy are seen on physical examination. Which one of the following viruses is LEAST likely to cause this picture?

(A) Norovirus

(B) Adenovirus

(C) Coxsackie virus

(D) Epstein–Barr virus

230. Scrapie and kuru possess all of the following characteristics EXCEPT:

(A) A histologic picture of spongiform encephalopathy

(B) Transmissibility to animals associated with a long incubation period

(C) Slowly progressive deterioration of brain function

(D) Prominent intranuclear inclusions in oligodendrocytes

231. Each of the following statements concerning subacute sclerosing panencephalitis is correct EXCEPT:

(A) Immunosuppression is a frequent predisposing factor.

(B) Aggregates of helical nucleocapsids are found in infected cells.

(C) High titers of measles antibody are found in cerebrospinal fluid.

(D) Gradual progressive deterioration of brain function occurs.

232. The slow virus disease that MOST clearly has immunosuppression as an important factor in its pathogenesis is:

(A) Progressive multifocal leukoencephalopathy

(B) Subacute sclerosing panencephalitis

(C) Creutzfeldt-Jakob disease

(D) Kuru

233. A 30-year-old man develops fever and jaundice. He consults a physician, who finds that blood tests for HBs antigen and anti-HBs antibody are negative. Which one of the following additional tests is MOST useful to establish that the hepatitis was indeed due to hepatitis B virus?

(A) HBe antigen

(B) Anti-HBc antibody

(C) Anti-HBe antibody

(D) Delta antigen

234. Which one of the following is the MOST reasonable explanation for the ability of hepatitis B virus to cause chronic infection?

(A) Infection does not elicit the production of antibody.

(B) The liver is an “immunologically sheltered” site.

(C) Viral DNA can persist within the host cell.

(D) Many humans are immunologically tolerant to HBs antigen.

235. The routine screening of transfused blood for HBs antigen has not eliminated the problem of post-transfusion hepatitis. For which one of the following viruses has screening eliminated a large number of cases of post-transfusion hepatitis?

(A) Hepatitis A virus

(B) Hepatitis C virus

(C) Cytomegalovirus

(D) Epstein–Barr virus

236. A 35-year-old man addicted to intravenous drugs has been a carrier of HBs antigen for 10 years. He suddenly develops acute fulminant hepatitis and dies within 10 days. Which one of the following laboratory tests would contribute MOST to a diagnosis?

(A) Anti-HBs antibody

(B) HBe antigen

(C) Anti-HBc antibody

(D) Anti-delta virus antibody

237. Which one of the following is the BEST evidence on which to base a decisive diagnosis of acute mumps disease?

(A) A positive skin test

(B) A fourfold rise in antibody titer to mumps antigen

(C) A history of exposure to a child with mumps

(D) Orchitis in young adult male

238. Varicella-zoster virus and herpes simplex virus share many characteristics. Which one of the following characteristics is NOT shared?

(A) Inapparent disease, manifested only by virus shedding, is common

(B) Persistence of latent virus after recovery from acute disease

(C) Vesicular rash

(D) Linear, double-stranded DNA genome

239. Herpes simplex virus and cytomegalovirus share many features. Which one of the following features is LEAST likely to be shared?

(A) Important cause of morbidity and mortality in the newborn

(B) Congenital abnormalities due to transplacental passage

(C) Important cause of serious disease in immunosuppressed individuals

(D) Mild or inapparent infection

240. The eradication of smallpox was facilitated by several features of the virus. Which one of the following contributed LEAST to eradication?

(A) It has one antigenic type.

(B) Inapparent infection is rare.

(C) Administration of live vaccine reliably induces immunity.

(D) It multiplies in the cytoplasm of infected cells.

241. Which one of the following statements concerning infectious mononucleosis is the MOST accurate?

(A) Multinucleated giant cells are found in the skin lesions.

(B) Infected T lymphocytes are abundant in peripheral blood.

(C) Isolation of virus is necessary to confirm the diagnosis.

(D) Infectious mononucleosis is transmitted by virus in saliva.

242. Which one of the following statements about genital herpes is LEAST accurate?

(A) Acyclovir reduces the number of recurrent disease episodes by eradicating latently infected cells.

(B) Genital herpes can be transmitted in the absence of apparent lesions.

(C) Multinucleated giant cells with intranuclear inclusions are found in the lesions.

(D) Initial disease episodes are generally more severe than recurrent episodes.

243. There are several influenza vaccines administered in the United States. Regarding these vaccines, which one of the following statements is LEAST accurate?

(A) One of the vaccines contains purified peptide subunits of neuraminidase produced in yeast.

(B) One of the vaccines is an inactivated vaccine consisting of formaldehyde-treated influenza virions.

(C) One of the vaccines contains a temperature-sensitive mutant of influenza virus that replicates in the nose but not in the lungs.

(D) Influenza vaccines contain influenza A and B strains but not C strains.

244. Which of the following is the MOST common lower respiratory pathogen in infants?

(A) Respiratory syncytial virus

(B) Adenovirus

(C) Rhinovirus

(D) Coxsackie virus

245. Which of the following conditions is LEAST likely to be caused by adenoviruses?

(A) Conjunctivitis

(B) Pneumonia

(C) Pharyngitis

(D) Glomerulonephritis

246. Regarding the serologic diagnosis of infectious mononucleosis, which one of the following is CORRECT?

(A) A heterophil antibody is formed that reacts with a capsid protein of Epstein–Barr virus.

(B) A heterophil antibody is formed that agglutinates sheep or horse red blood cells.

(C) A heterophil antigen occurs that cross-reacts with Proteus OX19 strains.

(D) A heterophil antigen occurs following infection with cytomegalovirus.

247. Herpes simplex virus type 1 (HSV-1) is distinct from HSV-2 in several different ways. Which one of the following is the LEAST accurate statement?

(A) HSV-1 causes lesions above the umbilicus more frequently than HSV-2 does.

(B) Infection by HSV-1 is not associated with any tumors in humans.

(C) Antiserum to HSV-1 neutralizes HSV-1 much more effectively than HSV-2.

(D) HSV-1 causes frequent recurrences, whereas HSV-2 infection rarely recurs.

248. Which one of the following statements about the src gene and src protein of Rous sarcoma virus is INCORRECT?

(A) The src protein inactivates a protein encoded by p53, a tumor suppressor gene.

(B) The src protein is a protein kinase that preferentially phosphorylates tyrosine in cellular proteins.

(C) The src protein is required to maintain neoplastic transformation of infected cells.

(D) The viral src gene is derived from a cellular gene found in many vertebrate species.

249. Each of the following statements supports the idea that cellular proto-oncogenes participate in human carcinogenesis EXCEPT:

(A) The c-abl gene is rearranged on the Philadelphia chromosome in myeloid leukemias and encodes a protein with increased tyrosine kinase activity.

(B) The N-myc gene is amplified as much as 100-fold in many advanced cases of neuroblastoma.

(C) The receptor for platelet-derived growth factor is a transmembrane protein that exhibits tyrosine kinase activity.

(D) The c-Ha-ras gene is mutated at specific codons in several types of human cancer.

250. Each of the following statements concerning human immunodeficiency virus (HIV) is correct EXCEPT:

(A) Screening tests for antibodies are useful to prevent transmission of HIV through transfused blood.

(B) The opportunistic infections seen in AIDS are primarily the result of a loss of cell-mediated immunity.

(C) Zidovudine (azidothymidine) inhibits the RNA-dependent DNA polymerase.

(D) The presence of circulating antibodies that neutralize HIV is evidence that an individual is protected against HIV-induced disease.

251. Which one of the following statements concerning viral meningitis and viral encephalitis is CORRECT?

(A) Herpes simplex virus type 2 is the leading cause of viral meningitis.

(B) Herpes simplex virus type 1 is an important cause of viral encephalitis.

(C) The spinal fluid protein is usually decreased in viral meningitis.

(D) The diagnosis of viral meningitis can be made by using the India ink stain on a sample of spinal fluid.

252. Each of the following statements is correct EXCEPT:

(A) Coxsackie viruses are enteroviruses and can replicate in both the respiratory and gastrointestinal tracts.

(B) Influenza viruses have multiple serotypes based on hemagglutinin and neuraminidase proteins located on the envelope surface.

(C) Flaviviruses are RNA enveloped viruses that replicate in animals as well as humans.

(D) Adenoviruses are RNA enveloped viruses that are an important cause of sexually transmitted disease.

253. Which one of the following statements concerning the prevention of viral disease is CORRECT?

(A) Adenovirus vaccine contains purified penton fibers and is usually given to children in conjunction with polio vaccine.

(B) Coxsackie virus vaccine contains live virus that induces IgA, which prevents reinfection by homologous serotypes.

(C) Flavivirus immunization consists of hyperimmune serum plus a vaccine consisting of subunits containing the surface glycoprotein.

(D) One of the influenza virus vaccines contains killed virus that induces neutralizing antibody directed against the hemagglutinin.

254. Each of the following statements concerning hepatitis C virus (HCV) and hepatitis D virus (HDV) is correct EXCEPT:

(A) HCV is an RNA virus that causes post-transfusion hepatitis.

(B) HDV is a defective virus that can replicate only in a cell that is also infected with hepatitis B virus.

(C) HDV is transmitted primarily by the fecal–oral route.

(D) People infected with HCV commonly become chronic carriers of HCV and are predisposed to hepatocellular carcinoma.

255. Each of the following statements concerning measles virus is correct EXCEPT:

(A) Measles virus is an enveloped virus with a single-stranded RNA genome.

(B) One of the important complications of measles is encephalitis.

(C) The initial site of measles virus replication is the upper respiratory tract, from which it spreads via the blood to the skin.

(D) Latent infection by measles virus can be explained by the integration of provirus into the host cell DNA.

256. Each of the following statements concerning measles vaccine is correct EXCEPT:

(A) The vaccine contains live, attenuated virus.

(B) The vaccine should not be given at the same time as the mumps vaccine because the immune system cannot respond to two viral antigens given at the same time.

(C) Virus in the vaccine contains only one serotype.

(D) The vaccine should not be given prior to 15 months of age because maternal antibodies can prevent an immune response.

257. Each of the following statements concerning rubella is correct EXCEPT:

(A) Congenital abnormalities occur primarily when a pregnant woman is infected during the first trimester.

(B) Women who say that they have never had rubella can, nevertheless, have neutralizing antibody in their serum.

(C) In a 6-year-old child, rubella is a mild, self-limited disease with few complications.

(D) Acyclovir is effective in the treatment of congenital rubella syndrome.

258. Each of the following statements concerning rabies and rabies virus is correct EXCEPT:

(A) The virus has a lipoprotein envelope and single-stranded RNA as its genome.

(B) The virus has a single antigenic type (serotype).

(C) In the United States, dogs are the most common reservoir.

(D) The incubation period is usually long (several weeks) rather than short (several days).

259. Each of the following statements concerning arboviruses is correct EXCEPT:

(A) The pathogenesis of dengue hemorrhagic shock syndrome is associated with the heterotypic anamnestic response.

(B) Wild birds are the reservoir for encephalitis viruses but not for yellow fever virus.

(C) Ticks are the main mode of transmission for both encephalitis viruses and yellow fever virus.

(D) There is a live, attenuated vaccine that effectively prevents yellow fever.

260. Each of the following statements concerning rhinoviruses is correct EXCEPT:

(A) Rhinoviruses are picornaviruses (i.e., small, nonenveloped viruses with an RNA genome).

(B) Rhinoviruses are an important cause of lower respiratory tract infections, especially in patients with chronic obstructive pulmonary disease.

(C) Rhinoviruses do not infect the gastrointestinal tract because they are inactivated by the acid pH in the stomach.

(D) There is no vaccine against rhinoviruses because they have too many antigenic types.

261. Each of the following statements concerning herpes simplex virus type 2 (HSV-2) is correct EXCEPT:

(A) Primary infection with HSV-2 does not confer immunity to primary infection with HSV-1.

(B) HSV-2 causes vesicular lesions, typically in the genital area.

(C) HSV-2 can cause alterations of the cell membrane, leading to cell fusion and the formation of multinucleated giant cells.

(D) Recurrent disease episodes due to reactivation of latent HSV-2 are usually more severe than the primary episode.

262. Each of the following statements concerning Epstein–Barr virus is correct EXCEPT:

(A) Many infections are mild or inapparent.

(B) The earlier in life primary infection is acquired, the more likely the typical picture of infectious mononucleosis will be manifest.

(C) Latently infected lymphocytes regularly persist following an acute episode of infection.

(D) Infection confers immunity against second episodes of infectious mononucleosis.

263. Each of the following statements regarding rotaviruses is correct EXCEPT:

(A) The rotavirus vaccine contains recombinant RNA polymerase as the immunogen.

(B) Rotaviruses are a leading cause of diarrhea in young children.

(C) Rotaviruses are transmitted primarily by the fecal–oral route.

(D) Rotaviruses belong to the reovirus family, which have a double-stranded, segmented RNA genome.

264. Each of the following statements concerning the antigenicity of influenza A virus is correct EXCEPT:

(A) Antigenic shifts, which represent major changes in antigenicity, occur infrequently and are due to the reassortment of segments of the viral genome.

(B) Antigenic shifts affect both the hemagglutinin and the neuraminidase.

(C) The worldwide epidemics caused by influenza A virus are due to antigenic shifts.

(D) The protein involved in antigenic drift is primarily the internal ribonucleoprotein.

265. Each of the following statements concerning adenoviruses is correct EXCEPT:

(A) Adenoviruses are composed of a double-stranded DNA genome and a capsid without an envelope.

(B) Adenoviruses cause both sore throat and pneumonia.

(C) Adenoviruses have only one serologic type.

(D) Adenoviruses are implicated as a cause of tumors in animals but not humans.

266. Each of the following statements concerning the prevention of viral respiratory tract disease is correct EXCEPT:

(A) To prevent disease caused by adenoviruses, a live enteric-coated vaccine that causes asymptomatic enteric infection is used in the military.

(B) To prevent disease caused by influenza A virus, an inactivated vaccine is available for the civilian population.

(C) There is no vaccine available against respiratory syncytial virus.

(D) To prevent disease caused by rhinoviruses, a vaccine containing purified capsid proteins is used.

267. Each of the following statements concerning herpesvirus latency is correct EXCEPT:

(A) Exogenous stimuli can cause reactivation of herpesvirus replication in latently-infected cells.

(B) During latency, antiviral antibody is not demonstrable in the sera of infected individuals.

(C) Reactivation of latent herpesviruses are more common in patients with impaired cell-mediated immunity than in immunocompetent patients.

(D) Herpesvirus genome DNA persists in latently infected cells.

268. Each of the following statements concerning rhinoviruses is correct EXCEPT:

(A) Rhinoviruses are the most common cause of the common cold.

(B) Rhinoviruses grow better at 33°C than at 37°C; hence they tend to cause disease in the upper respiratory tract rather than the lower respiratory tract.

(C) Rhinoviruses are members of the picornaviruses family and hence resemble poliovirus in their structure and replication.

(D) The immunity provided by the rhinovirus vaccine is excellent because there is only one serotype.

269. Which one of the following statements concerning poliovirus infection is CORRECT?

(A) Congenital infection of the fetus is an important complication.

(B) The virus replicates extensively in the gastrointestinal tract.

(C) A skin test is available to determine prior exposure to the virus.

(D) Amantadine is an effective preventive agent.

270. Each of the following statements concerning yellow fever is correct EXCEPT:

(A) Yellow fever virus is transmitted by the Aedes aegypti mosquito in the urban form of yellow fever.

(B) Infection by yellow fever virus causes significant damage to hepatocytes.

(C) Nonhuman primates in the jungle are a major reservoir of yellow fever virus.

(D) Acyclovir is an effective treatment for yellow fever.

271. Which one of the following statements concerning mumps is CORRECT?

(A) Although the salivary glands are the most obvious sites of infection, the testes, ovaries, and pancreas can be involved as well.

(B) Because there is no vaccine against mumps, passive immunization is the only means of preventing the disease.

(C) The diagnosis of mumps is made on clinical grounds because the virus cannot be grown in cell culture and serologic tests are inaccurate.

(D) Second episodes of mumps can occur because there are two serotypes of the virus and protection is type-specific.

272. Many of the oncogenic retroviruses carry oncogenes closely related to normal cellular genes, called proto-oncogenes. Which one of the following statements concerning proto-oncogenes is INCORRECT?

(A) Several proto-oncogenes have been found in mutant form in human cancers that lack evidence for viral etiology.

(B) Several viral oncogenes and their progenitor proto-oncogenes encode protein kinases specific for tyrosine.

(C) Some proto-oncogenes encode cellular growth factors and receptors for growth factors.

(D) Proto-oncogenes are closely related to transposons found in bacteria.

273. Each of the following statements concerning human immunodeficiency virus is correct EXCEPT:

(A) The CD4 protein on the T-cell surface is one of the receptors for the virus.

(B) There is appreciable antigenic diversity in the envelope glycoprotein of the virus.

(C) One of the viral genes codes for a protein that augments the activity of the viral transcriptional promoter.

(D) A major problem with testing for antibody to the virus is its cross-reactivity with human T-cell lymphoma virus type I.

274. Each of the following statements concerning human immunodeficiency virus (HIV) is correct EXCEPT:

(A) Patients infected with HIV typically form antibodies against both the envelope glycoproteins (gp120 and gp41) and the internal group-specific antigen (p24).

(B) HIV probably arose as an endogenous virus of humans because HIV proviral DNA is found in the DNA of certain normal human cells.

(C) Transmission of HIV occurs primarily by the transfer of blood or semen in adults, and neonates can be infected at the time of delivery.

(D) The Western blot test is more specific for HIV infection than the ELISA is.

275. Each of the following statements concerning hepatitis A virus (HAV) is correct EXCEPT:

(A) The hepatitis A vaccine contains inactivated HAV as the immunogen.

(B) HAV commonly causes asymptomatic infection in children.

(C) The diagnosis of hepatitis A is usually made by isolating HAV in cell culture.

(D) Gamma globulin is used to prevent hepatitis A in exposed persons.

Answers (Questions 212–275)

212. (C)

213. (B)

214. (B)

215. (D)

216. (C)

217. (B)

218. (A)

219. (D)

220. (A)

221. (D)

222. (C)

223. (C)

224. (D)

225. (B)

226. (D)

227. (D)

228. (B)

229. (A)

230. (D)

231. (A)

232. (A)

233. (B)

234. (C)

235. (B)

236. (D)

237. (B)

238. (A)

239. (B)

240. (D)

241. (D)

242. (A)

243. (A)

244. (A)

245. (D)

246. (B)

247. (D)

248. (A)

249. (C)

250. (D)

251. (B)

252. (D)

253. (D)

254. (C)

255. (D)

256. (B)

257. (D)

258. (C)

259. (C)

260. (B)

261. (D)

262. (B)

263. (A)

264. (D)

265. (C)

266. (D)

267. (B)

268. (D)

269. (B)

270. (D)

271. (A)

272. (D)

273. (D)

274. (B)

275. (C)

DIRECTIONS (Questions 276–294): Select the ONE lettered option that is MOST closely associated with the numbered items. Each lettered option may be selected once, more than once, or not at all.

Questions 276–279

(A) Yellow fever virus

(B) Rabies virus

(C) Rotavirus

(D) Rubella virus

(E) Rhinovirus

276. Diarrhea

277. Jaundice

278. Congenital abnormalities

279. Encephalitis

Questions 280–284

(A) Bronchiolitis

(B) Meningitis

(C) Pharyngitis

(D) Shingles

(E) Subacute sclerosing panencephalitis

280. Adenovirus

281. Measles virus

282. Respiratory syncytial virus

283. Coxsackie virus

284. Varicella-zoster virus

Questions 285–289

(A) Adenovirus

(B) Parainfluenza virus

(C) Rhinovirus

(D) Coxsackie virus

(E) Epstein–Barr virus

285. Causes myocarditis and pleurodynia

286. Grows better at 33°C than 37°C

287. Causes tumors in laboratory rodents

288. Causes croup in young children

289. Causes infectious mononucleosis

Questions 290–294

(A) Hepatitis C virus

(B) Cytomegalovirus

(C) Human papillomavirus

(D) Dengue virus

(E) St. Louis encephalitis virus

290. It is implicated as the cause of carcinoma of the cervix.

291. Wild birds are an important reservoir.

292. It is an important cause of pneumonia in immunocompromised patients.

293. Donated blood containing antibody to this RNA virus should not be used for transfusion.

294. It causes a hemorrhagic fever that can be life-threatening.

Answers (Questions 276–294)

276. (C)

277. (A)

278. (D)

279. (B)

280. (C)

281. (E)

282. (A)

283. (B)

284. (D)

285. (D)

286. (C)

287. (A)

288. (B)

289. (E)

290. (C)

291. (E)

292. (B)

293. (A)

294. (D)

MYCOLOGY

DIRECTIONS (Questions 295–317): Select the ONE lettered answer that is BEST in each question.

295. Which one of the following fungi is MOST likely to be found within reticuloendothelial cells?

(A) Histoplasma capsulatum

(B) Candida albicans

(C) Cryptococcus neoformans

(D) Sporothrix schenckii

296. Your patient is a woman with a vaginal discharge. You suspect, on clinical grounds, that it may be due to Candida albicans. Which one of the following statements is LEAST accurate or appropriate?

(A) A Gram stain of the discharge should reveal budding yeasts.

(B) Culture of the discharge on Sabouraud’s agar should produce a white mycelium with aerial conidia.

(C) The clinical laboratory can use germ tube formation to identify the isolate as C. albicans.

(D) Antibiotics predispose to Candida vaginitis by killing the normal flora lactobacilli that keep the vaginal pH low.

297. You have made a clinical diagnosis of meningitis in a 50-year-old immunocompromised woman. A latex agglutination test on the spinal fluid for capsular polysaccharide antigen is positive. Of the following organisms, which one is the MOST likely cause?

(A) Histoplasma capsulatum

(B) Cryptococcus neoformans

(C) Aspergillus fumigatus

(D) Candida albicans

298. Fungi often colonize lesions due to other causes. Which one of the following is LEAST likely to be present as a colonizer?

(A) Aspergillus

(B) Mucor

(C) Sporothrix

(D) Candida

299. Your patient complains of an “itching rash” on her abdomen. On examination, you find that the lesions are red, circular, with a vesiculated border and a healing central area. You suspect tinea corporis. Of the following choices, the MOST appropriate laboratory procedure to make the diagnosis is a:

(A) Potassium hydroxide mount of skin scrapings

(B) Giemsa stain for multinucleated giant cells

(C) Fluorescent antibody stain of the vesicle fluid

(D) Fourfold rise in antibody titer against the organism

300. Each of the following statements concerning Cryptococcus neoformans is correct EXCEPT:

(A) Its natural habitat is the soil, especially associated with pigeon feces.

(B) Pathogenesis is related primarily to the production of exotoxin A.

(C) Budding yeasts are found in the lesions.

(D) The initial site of infection is usually the lung.

301. A woman who pricked her finger while pruning some rose bushes develops a local pustule that progresses to an ulcer. Several nodules then develop along the local lymphatic drainage. The MOST likely agent is:

(A) Cryptococcus neoformans

(B) Candida albicans

(C) Sporothrix schenckii

(D) Aspergillus fumigatus

302. Several fungi are associated with disease in immunocompromised patients. Which one of the following is the LEAST frequently associated?

(A) Cryptococcus neoformans

(B) Aspergillus fumigatus

(C) Malassezia furfur

(D) Mucor species

303. Fungal cells that reproduce by budding are seen in the infected tissues of patients with:

(A) Candidiasis, cryptococcosis, and sporotrichosis

(B) Mycetoma, candidiasis, and mucormycosis

(C) Tinea corporis, tinea unguium, and tinea versicolor

(D) Sporotrichosis, mycetoma, and aspergillosis

304. Infection by a dermatophyte is MOST often associated with:

(A) Intravenous drug abuse

(B) Inhalation of the organism from contaminated bird feces

(C) Adherence of the organism to perspiration-moist skin

(D) Fecal–oral transmission

305. Aspergillosis is recognized in tissue by the presence of:

(A) Budding cells

(B) Septate hyphae

(C) Metachromatic granules

(D) Pseudohyphae

306. Which one of the following is NOT a characteristic of histoplasmosis?

(A) Person-to-person transmission

(B) Specific geographic distribution

(C) Yeasts in the tissue

(D) Mycelial phase in the soil

307. Each of the following statements concerning mucormycosis is correct EXCEPT:

(A) The fungi that cause mucormycosis are transmitted by airborne asexual spores.

(B) Tissue sections from a patient with mucormycosis show budding yeasts.

(C) Hyphae typically invade blood vessels and cause necrosis of tissue.

(D) Ketoacidosis in diabetic patients is a predisposing factor to mucormycosis.

308. Each of the following statements concerning fungi is correct EXCEPT:

(A) Yeasts are fungi that reproduce by budding.

(B) Molds are fungi that have elongated filaments called hyphae.

(C) Thermally dimorphic fungi exist as yeasts at 37°C and as molds at 25°C.

(D) Both yeasts and molds have a cell wall made of peptidoglycan.

309. Each of the following statements concerning yeasts is correct EXCEPT:

(A) Yeasts have chitin in their cell walls and ergosterol in their cell membranes.

(B) Yeasts form ascospores when they invade tissue.

(C) Yeasts have eukaryotic nuclei and contain mitochondria in their cytoplasm.

(D) Yeasts produce neither endotoxin nor exotoxins.

310. Each of the following statements concerning fungi and protozoa is correct EXCEPT:

(A) Both fungi and protozoa are eukaryotic organisms.

(B) Fungi possess a cell wall, whereas protozoa do not.

(C) Both fungi and protozoa use flagella as their organ of motility.

(D) Both fungi and protozoa generate energy in mitochondria.

311. You suspect that your patient’s disease may be caused by Cryptococcus neoformans. Which one of the following findings would be MOST useful in establishing the diagnosis?

(A) A positive heterophil agglutination test for the presence of antigen

(B) A history of recent travel in the Mississippi River valley area

(C) The finding of encapsulated budding cells in spinal fluid

(D) Recovery of an acid-fast organism from the patient’s sputum

312. Each of the following statements concerning Candida albicans is correct EXCEPT:

(A) C. albicans is a budding yeast that forms pseudohyphae when it invades tissue.

(B) C. albicans is transmitted primarily by respiratory aerosol.

(C) C. albicans causes thrush.

(D) Impaired cell-mediated immunity is an important predisposing factor to disease.

313. Each of the following statements concerning Coccidioides immitis is correct EXCEPT:

(A) The mycelial phase of the organism grows primarily in the soil, which is its natural habitat.

(B) In the body, spherules containing endospores are formed.

(C) A rising titer of complement-fixing antibody indicates disseminated disease.

(D) Most infections are symptomatic and require treatment with amphotericin B.

314. Each of the following statements concerning Histoplasma capsulatum is correct EXCEPT:

(A) The natural habitat of H. capsulatum is the soil, where it grows as a mold.

(B) H. capsulatum is transmitted by airborne conidia, and its initial site of infection is the lung.

(C) Within the body, H. capsulatum grows primarily intracellularly within macrophages.

(D) Passive immunity in the form of high titer antibodies should be given to those known to be exposed.

315. Each of the following statements concerning infection caused by Coccidioides immitis is correct EXCEPT:

(A) C. immitis is a dimorphic fungus.

(B) C. immitis is acquired by inhalation of arthrospores.

(C) More than 50% of clinical isolates are resistant to amphotericin B.

(D) Infection occurs primarily in the southwestern states and California.

316. Each of the following statements concerning Blastomyces dermatitidis is correct EXCEPT:

(A) B. dermatitidis grows as a mold in the soil in North America.

(B) B. dermatitidis is a dimorphic fungus that forms yeast cells in tissue.

(C) B. dermatitidis infection is commonly diagnosed by serologic tests because it does not grow in culture.

(D) B. dermatitidis causes granulomatous skin lesions.

317Aspergillus fumigatus can be involved in a variety of clinical conditions. Which one of the following is LEAST likely to occur?

(A) Tissue invasion in immunocompromised host

(B) Allergy following inhalation of airborne particles of the fungus

(C) Colonization of tuberculous cavities in the lung

(D) Thrush

Answers (Questions 295–317)

295. (A)

296. (B)

297. (B)

298. (C)

299. (A)

300. (B)

301. (C)

302. (C)

303. (A)

304. (C)

305. (B)

306. (A)

307. (B)

308. (D)

309. (B)

310. (C)

311. (C)

312. (B)

313. (D)

314. (D)

315. (C)

316. (C)

317. (D)

DIRECTIONS (Questions 318–325): Select the ONE lettered option that is MOST closely associated with the numbered items. Each lettered option may be selected once, more than once, or not at all.

Questions 318–321

(A) Histoplasma capsulatum

(B) Candida albicans

(C) Aspergillus fumigatus

(D) Sporothrix schenckii

318. A budding yeast that is a member of the normal flora of the vagina

319. A dimorphic organism that is transmitted by trauma to the skin

320. A dimorphic fungus that typically is acquired by inhalation of asexual spores

321. A mold that causes pneumonia in immunocompromised patients

Questions 322–325

(A) Coccidioides immitis

(B) Rhizopus nigricans

(C) Blastomyces dermatitidis

(D) Cryptococcus neoformans

322. A yeast acquired by inhalation that causes meningitis primarily in immunocompromised patients

323. A mold that invades blood vessels primarily in patients with diabetic ketoacidosis

324. A dimorphic fungus that is acquired by inhalation by people living in certain areas of the southwestern states in the United States

325. A dimorphic fungus that causes granulomatous skin lesions in people living throughout North America

Answers (Questions 318–325)

318. (B)

319. (D)

320. (A)

321. (C)

322. (D)

323. (B)

324. (A)

325. (C)

PARASITOLOGY

DIRECTIONS (Questions 326–352): Select the ONE lettered answer that is BEST in each question.

326. Children at day care centers in the United States have a high rate of infection with which one of the following?

(A) Ascaris lumbricoides

(B) Entamoeba histolytica

(C) Enterobius vermicularis

(D) Necator americanus

327. The main anatomic location of Schistosoma mansoni adult worms is:

(A) Lung alveoli

(B) Intestinal venules

(C) Renal tubules

(D) Bone marrow

328. In malaria, the form of plasmodia that is transmitted from mosquito to human is the:

(A) Sporozoite

(B) Gametocyte

(C) Merozoite

(D) Hypnozoite

329. Which one of the following protozoa primarily infects macrophages?

(A) Plasmodium vivax

(B) Leishmania donovani

(C) Trypanosoma cruzi

(D) Trichomonas vaginalis

330. Each of the following parasites has an intermediate host as part of its life cycle EXCEPT:

(A) Trichomonas vaginalis

(B) Taenia solium

(C) Echinococcus granulosus

(D) Toxoplasma gondii

331. Each of the following parasites passes through the lung during human infection EXCEPT:

(A) Strongyloides stercoralis

(B) Necator americanus

(C) Wuchereria bancrofti

(D) Ascaris lumbricoides

332. Each of the following parasites is transmitted by flies EXCEPT:

(A) Schistosoma mansoni

(B) Onchocerca volvulus

(C) Trypanosoma gambiense

(D) Loa loa

333. Each of the following parasites is transmitted by mosquitoes EXCEPT:

(A) Leishmania donovani

(B) Wuchereria bancrofti

(C) Plasmodium vivax

(D) Plasmodium falciparum

334. Pigs or dogs are the source of human infection by each of the following parasites EXCEPT:

(A) Echinococcus granulosus

(B) Taenia solium

(C) Ascaris lumbricoides

(D) Trichinella spiralis

335. Each of the following parasites is transmitted by eating inadequately cooked fish or seafood EXCEPT:

(A) Diphyllobothrium latum

(B) Ancylostoma duodenale

(C) Paragonimus westermani

(D) Clonorchis sinensis

336. Laboratory diagnosis of a patient with a suspected liver abscess due to Entamoeba histolytica should include:

(A) Stool examination and indirect hemagglutination test

(B) Stool examination and blood smear

(C) Indirect hemagglutination test and skin test

(D) Xenodiagnosis and string test

337. Each of the following statements concerning Toxoplasma gondii is correct EXCEPT:

(A) T. gondii can be transmitted across the placenta to the fetus.

(B) T. gondii can be transmitted by cat feces.

(C) T. gondii can cause encephalitis in immunocompromised patients.

(D) T. gondii can be diagnosed by finding trophozoites in the stool.

338. Each of the following statements concerning Giardia lamblia is correct EXCEPT:

(A) G. lamblia has both a trophozoite and a cyst stage in its life cycle.

(B) G. lamblia is transmitted by the fecal–oral route from both human and animal sources.

(C) G. lamblia causes hemolytic anemia.

(D) G. lamblia can be diagnosed by the string test in which a weighted string is swallowed and passes into the upper GI tract.

339. Each of the following statements concerning malaria is correct EXCEPT:

(A) The female Anopheles mosquito is the vector.

(B) Early in infection, sporozoites enter hepatocytes.

(C) Release of merozoites from red blood cells causes periodic fever and chills.

(D) The principal site of gametocyte formation is the human gastrointestinal tract.

340. Each of the following statements concerning Trichomonas vaginalis is correct EXCEPT:

(A) T. vaginalis is transmitted sexually.

(B) T. vaginalis can be diagnosed by visualizing the trophozoite.

(C) T. vaginalis can be treated effectively with metronidazole.

(D) T. vaginalis causes bloody diarrhea.

341. Which one of the following agents can be used to prevent malaria?

(A) Mebendazole

(B) Chloroquine

(C) Inactivated vaccine

(D) Praziquantel

342. Each of the following statements concerning Pneumocystis carinii is correct EXCEPT:

(A) P. carinii infections primarily involve the respiratory tract.

(B) P. carinii can be diagnosed by seeing cysts in tissue.

(C) P. carinii infections are symptomatic primarily in immunocompromised patients.

(D) P. carinii symptomatic infections can be prevented by administering penicillin orally.

343. Each of the following statements concerning Trypanosoma cruzi is correct EXCEPT:

(A) T. cruzi is transmitted by the reduviid bug.

(B) T. cruzi occurs primarily in tropical Africa.

(C) T. cruzi can be diagnosed by seeing amastigotes in a bone marrow aspirate.

(D) T. cruzi typically affects heart muscle, leading to cardiac failure.

344. Each of the following statements concerning sleeping sickness is correct EXCEPT:

(A) Sleeping sickness is caused by a trypanosome.

(B) Sleeping sickness is transmitted by tsetse flies.

(C) Sleeping sickness can be diagnosed by finding eggs in the stool.

(D) Sleeping sickness occurs primarily in tropical Africa.

345. Each of the following statements concerning kala-azar is correct EXCEPT:

(A) Kala-azar is caused by Leishmania donovani.

(B) Kala-azar is transmitted by the bite of sandflies.

(C) Kala-azar occurs primarily in rural Latin America.

(D) Kala-azar can be diagnosed by finding amastigotes in bone marrow.

346. Each of the following statements concerning Diphyllobothrium latum is correct EXCEPT:

(A) D. latum is transmitted by undercooked fish.

(B) D. latum has operculated eggs.

(C) D. latum causes a megaloblastic anemia due to vitamin B12 deficiency.

(D) D. latum is a tapeworm that has a scolex with a circle of hooks.

347. Each of the following statements concerning hydatid cyst disease is correct EXCEPT:

(A) The disease is caused by Echinococcus granulosus.

(B) The cysts occur primarily in the liver.

(C) The disease is caused by a parasite whose adult form lives in dogs’ intestines.

(D) The disease occurs primarily in tropical Africa.

348. Each of the following statements concerning Schistosoma haematobium is correct EXCEPT:

(A) S. haematobium is acquired by humans when cercariae penetrate the skin.

(B) Snails are intermediate hosts of S. haematobium.

(C) S. haematobium eggs have no spine.

(D) S. haematobium infection predisposes to bladder carcinoma.

349. Each of the following statements concerning hookworm infection is correct EXCEPT:

(A) Hookworm infection can cause anemia.

(B) Hookworm infection is acquired by humans when filariform larvae penetrate the skin.

(C) Hookworm infection is caused by Necator americanus.

(D) Hookworm infection can be diagnosed by finding the trophozoite in the stool.

350. Each of the following statements concerning Ascaris lumbricoides is correct EXCEPT:

(A) A. lumbricoides is one of the largest nematodes.

(B) A. lumbricoides is transmitted by ingestion of eggs.

(C) Both dogs and cats are intermediate hosts of A. lumbricoides.

(D) A. lumbricoides can cause pneumonia.

351. Each of the following statements concerning Strongyloides stercoralis is correct EXCEPT:

(A) S. stercoralis is acquired by ingestion of eggs.

(B) S. stercoralis undergoes a free-living life cycle in soil.

(C) Migrating larvae of S. stercoralis induce a marked eosinophilia.

(D) S. stercoralis produces filariform larvae.

352. Each of the following statements concerning trichinosis is correct EXCEPT:

(A) Trichinosis is acquired by eating undercooked pork.

(B) Trichinosis is caused by a protozoan that has both a trophozoite and a cyst stage in its life cycle.

(C) Trichinosis can be diagnosed by seeing cysts in muscle biopsy specimens.

(D) Eosinophilia is a prominent finding.

Answers (Questions 326–352)

326. (C)

327. (B)

328. (A)

329. (B)

330. (A)

331. (C)

332. (A)

333. (A)

334. (C)

335. (B)

336. (A)

337. (D)

338. (C)

339. (D)

340. (D)

341. (B)

342. (D)

343. (B)

344. (C)

345. (C)

346. (D)

347. (D)

348. (C)

349. (D)

350. (C)

351. (A)

352. (B)

DIRECTIONS (Questions 353–386): Select the ONE lettered option that is MOST closely associated with the numbered items. Each lettered option may be selected once, more than once, or not at all.

Questions 353–360

(A) Dracunculus medinensis

(B) Loa loa

(C) Onchocerca volvulus

(D) Wuchereria bancrofti

(E) Toxocara canis

353. Causes river blindness

354. Transmitted by mosquito

355. Acquired by drinking contaminated water

356. Treated by extracting worm from skin ulcer

357. Transmitted by deer fly or mango fly

358. Causes visceral larva migrans

359. Causes filariasis

360. Acquired by ingestion of worm eggs

Questions 361–372

(A) Giardia lamblia

(B) Plasmodium vivax

(C) Taenia saginata

(D) Clonorchis sinensis

(E) Enterobius vermicularis

361. A trematode (fluke) acquired by eating undercooked fish

362. A cestode (tapeworm) acquired by eating undercooked beef

363. A nematode (roundworm) transmitted primarily from child to child

364. A protozoan transmitted by mosquito

365. A protozoan transmitted by the fecal–oral route

366. Primarily affects the biliary ducts

367. Causes diarrhea as the most prominent symptom

368. Causes perianal itching as the most prominent symptom

369. Causes fever, chills, and anemia

370. Can be treated with metronidazole

371. Can be treated with mebendazole or pyrantel pamoate

372. Can be treated with chloroquine and primaquine

Questions 373–386

(A) Entamoeba histolytica

(B) Plasmodium falciparum

(C) Taenia solium

(D) Paragonimus westermani

(E) Strongyloides stercoralis

373. A cestode (tapeworm) acquired by eating undercooked pork

374. A nematode (roundworm) acquired when filariform larvae penetrate the skin

375. A protozoan transmitted by the fecal–oral route

376. A trematode (fluke) acquired by eating undercooked crab meat

377. A protozoan that infects red blood cells

378. Laboratory diagnosis based on finding eggs in sputum

379. Causes cysticercosis in humans

380. Chloroquine-resistant strains occur

381. Autoinfection within humans, especially in immunocompromised patients

382. Causes blackwater fever

383. Causes bloody diarrhea and liver abscesses

384. Produces “banana-shaped” gametocytes

385. Produces cysts with four nuclei

386. Has a scolex with suckers and a circle of hooks

Answers (Questions 353–386)

353. (C)

354. (D)

355. (A)

356. (A)

357. (B)

358. (E)

359. (D)

360. (E)

361. (D)

362. (C)

363. (E)

364. (B)

365. (A)

366. (D)

367. (A)

368. (E)

369. (B)

370. (A)

371. (E)

372. (B)

373. (C)

374. (E)

375. (A)

376. (D)

377. (B)

378. (D)

379. (C)

380. (B)

381. (E)

382. (B)

383. (A)

384. (B)

385. (A)

386. (C)

IMMUNOLOGY

DIRECTIONS (Questions 387–474): Select the ONE lettered answer that is BEST in each question.

387. Which category of hypersensitivity BEST describes hemolytic disease of the newborn caused by Rh incompatibility?

(A) Atopic or anaphylactic

(B) Cytotoxic

(C) Immune complex

(D) Delayed

388. The principal difference between cytotoxic (type II) and immune complex (type III) hypersensitivity is:

(A) The class (isotype) of antibody

(B) Whether the antibody reacts with the antigen on the cell or reacts with antigen before it interacts with the cell

(C) The participation of complement

(D) The participation of T cells

389. A child stung by a bee experiences respiratory distress within minutes and lapses into unconsciousness. This reaction is probably mediated by:

(A) IgE antibody

(B) IgG antibody

(C) Sensitized T cells

(D) Complement

(E) IgM antibody

390. A patient with rheumatic fever develops a sore throat from which β-hemolytic streptococci are cultured. The patient is started on treatment with penicillin, and the sore throat resolves within several days. However, 7 days after initiation of penicillin therapy, the patient develops a fever of 103°F, a generalized rash, and proteinuria. This MOST probably resulted from:

(A) Recurrence of the rheumatic fever

(B) A different infectious disease

(C) An IgE response to penicillin

(D) An IgG-IgM response to penicillin

(E) A delayed hypersensitivity reaction to penicillin

391. A kidney biopsy specimen taken from a patient with acute glomerulonephritis and stained with fluorescein-conjugated anti-human IgG antibody would probably show:

(A) No fluorescence

(B) Uniform fluorescence of the glomerular basement membrane

(C) Patchy, irregular fluorescence of the glomerular basement membrane

(D) Fluorescent B cells

(E) Fluorescent macrophages

392. A patient with severe asthma gets no relief from antihistamines. The symptoms are MOST likely to be caused by:

(A) Interleukin-2

(B) Slow-reacting substance A (leukotrienes)

(C) Serotonin

(D) Bradykinin

393. Hypersensitivity to penicillin and hypersensitivity to poison oak are both:

(A) Mediated by IgE antibody

(B) Mediated by IgG and IgM antibody

(C) Initiated by haptens

(D) Initiated by Th-2 cells

394. A recipient of a two-haplotype MHC-matched kidney from a relative still needs immunosuppression to prevent graft rejection because:

(A) Graft-versus-host disease is a problem

(B) Class II MHC antigens will not be matched

(C) Minor histocompatibility antigens will not be matched

(D) Complement components will not be matched

395. Bone marrow transplantation in immunocompromised patients presents which major problem?

(A) Potentially lethal graft-versus-host disease

(B) High risk of T-cell leukemia

(C) Inability to use a live donor

(D) Delayed hypersensitivity

396. What is the role of class II MHC proteins on donor cells in graft rejection?

(A) They are the receptors for interleukin-2, which is produced by macrophages when they attack the donor cells.

(B) They are recognized by helper T cells, which then activate cytotoxic T cells to kill the donor cells.

(C) They induce the production of blocking antibodies that protect the graft.

(D) They induce IgE, which mediates graft rejection.

397. Grafts between genetically identical individuals (i.e., identical twins):

(A) Are rejected slowly as a result of minor histocompatibility antigens

(B) Are subject to hyperacute rejection

(C) Are not rejected, even without immunosuppression

(D) Are not rejected if a kidney is grafted, but skin grafts are rejected

398. Penicillin is a hapten in both humans and mice. To explore the hapten–carrier relationship, a mouse was injected with penicillin covalently bound to bovine serum albumin and, at the same time, with egg albumin to which no penicillin was bound. Of the following, which one will induce a secondary response to penicillin when injected into the mouse 1 month later?

(A) Penicillin

(B) Penicillin bound to egg albumin

(C) Egg albumin

(D) Bovine serum albumin

399. AIDS is caused by a human retrovirus that kills:

(A) B lymphocytes

(B) Lymphocyte stem cells

(C) CD4-positive T lymphocytes

(D) CD8-positive T lymphocytes

400. Chemically induced tumors have tumor-associated transplantation antigens that:

(A) Are always the same for a given carcinogen

(B) Are different for two tumors of different histologic type even if induced by the same carcinogen

(C) Are very strong antigens

(D) Do not induce an immune response

401. Polyomavirus (a DNA virus) causes tumors in “nude mice” (nude mice do not have a thymus because of a genetic defect) but not in normal mice. The BEST interpretation is that:

(A) Macrophages are required to reject polyomavirus-induced tumors

(B) Natural killer cells can reject polyomavirus-induced tumors without help from T lymphocytes

(C) T lymphocytes play an important role in the rejection of polyomavirus-induced tumors

(D) B lymphocytes play no role in rejection of polyomavirus-induced tumors

402. C3 is cleaved to form C3a and C3b by C3 convertase. C3b is involved in all of the following EXCEPT:

(A) Increasing vascular permeability

(B) Promoting phagocytosis

(C) Forming alternative-pathway C3 convertase

(D) Forming C5 convertase

403. After binding to its specific antigen, a B lymphocyte may switch its:

(A) Immunoglobulin light chain isotype

(B) Immunoglobulin heavy chain class

(C) Variable region of the immunoglobulin heavy chain

(D) Constant region of the immunoglobulin light chain

404. Diversity is an important feature of the immune system. Which one of the following statements about it is INCORRECT?

(A) Humans can make antibodies with about 108 different VH × VL combinations.

(B) A single cell can synthesize IgM antibody then switch to IgA antibody.

(C) The hematopoietic stem cell carries the genetic potential to create more than 104 immunoglobulin genes.

(D) A single B lymphocyte can produce antibodies of many different specificities, but a plasma cell is monospecific.

405. C3a and C5a can cause:

(A) Bacterial lysis

(B) Vascular permeability

(C) Phagocytosis of IgE-coated bacteria

(D) Aggregation of C4 and C2

406. Neutrophils are attracted to an infected area by:

(A) IgM

(B) C1

(C) C5a

(D) C8

407. Complement fixation refers to:

(A) The ingestion of C3b-coated bacteria by macrophages

(B) The destruction of complement in serum by heating at 56°C for 30 minutes

(C) The binding of complement components by antigen–antibody complexes

(D) The interaction of C3b with mast cells

408. The classic complement pathway is initiated by interaction of C1 with:

(A) Antigen

(B) Factor B

(C) Antigen–IgG complexes

(D) Bacterial lipopolysaccharides

409. Patients with severely reduced C3 levels tend to have:

(A) Increased numbers of severe viral infections

(B) Increased numbers of severe bacterial infections

(C) Low gamma globulin levels

(D) Frequent episodes of hemolytic anemia

410. Individuals with a genetic deficiency of C6 have:

(A) Decreased resistance to viral infections

(B) Increased hypersensitivity reactions

(C) Increased frequency of cancer

(D) Decreased resistance to Neisseria bacteremia

411. Natural killer cells are:

(A) B cells that can kill without complement

(B) Cytotoxic T cells

(C) Increased by immunization

(D) Able to kill virus-infected cells without prior sensitization

412. A positive tuberculin skin test (a delayed hypersensitivity reaction) indicates that:

(A) A humoral immune response has occurred

(B) A cell-mediated immune response has occurred

(C) Both the T-and B-cell systems are functional

(D) Only the B-cell system is functional

413. Reaction to poison ivy or poison oak is:

(A) An IgG-mediated response

(B) An IgE-mediated response

(C) A cell-mediated response

(D) An Arthus reaction

414. A child disturbs a wasp nest, is stung repeatedly, and goes into shock within minutes, manifesting respiratory failure and vascular collapse. This is MOST likely to be due to:

(A) Systemic anaphylaxis

(B) Serum sickness

(C) An Arthus reaction

(D) Cytotoxic hypersensitivity

415. “Isotype switching” of immunoglobulin classes by B cells involves:

(A) Simultaneous insertion of VH genes adjacent to each CH gene

(B) Successive insertion of a VH gene adjacent to different CH genes

(C) Activation of homologous genes on chromosome 6

(D) Switching of light chain types (kappa and lambda)

416. Which one of the following pairs of genes is linked on a single chromosome?

(A) V gene for lambda chain and C gene for kappa chain

(B) C gene for gamma chain and C gene for kappa chain

(C) V gene for lambda chain and V gene for heavy chain

(D) C gene for gamma chain and C gene for alpha chain

417. Idiotypic determinants are located within:

(A) Hypervariable regions of heavy and light chains

(B) Constant regions of light chains

(C) Constant regions of heavy chains

(D) The hinge region

418. A primary immune response in an adult human requires approximately how much time to produce detectable antibody levels in the blood?

(A) 12 hours

(B) 3 days

(C) 1 week

(D) 3 weeks

419. The membrane IgM and IgD on the surface of an individual B cell:

(A) Have identical heavy chains but different light chains

(B) Are identical except for their CH regions

(C) Are identical except for their VH regions

(D) Have different VH and VL regions

420. During the maturation of a B lymphocyte, the first immunoglobulin heavy chain synthesized is the:

(A) Mu chain

(B) Gamma chain

(C) Epsilon chain

(D) Alpha chain

421. In the immune response to a hapten–protein conjugate, in order to get anti-hapten antibodies, it is essential that:

(A) The hapten be recognized by helper T cells

(B) The protein be recognized by helper T cells

(C) The protein be recognized by B cells

(D) The hapten be recognized by suppressor T cells

422. In the determination of serum insulin levels by radioimmunoassay, which one of the following is NOT needed?

(A) Isotope-labeled insulin

(B) Anti-insulin antibody made in goats

(C) Anti-goat gamma globulin made in rabbits

(D) Isotope-labeled anti-insulin antibody made in goats

423. Which one of the following sequences is appropriate for testing a patient for antibody against the AIDS virus with the ELISA procedure? (The assay is carried out in a plastic plate with an incubation and a wash step after each addition except the final one.)

(A) Patient’s serum/enzyme substrate/HIV antigen/enzyme-labeled antibody against HIV

(B) HIV antigen/patient’s serum/enzyme-labeled antibody against human gamma globulin/enzyme substrate

(C) Enzyme-labeled antibody against human gamma globulin/patient’s serum/HIV antigen/enzyme substrate

(D) Enzyme-labeled antibody against HIV/HIV antigen/patient’s serum/enzyme substrate

424. The BEST method to demonstrate IgG on the glomerular basement membrane in a kidney tissue section is the:

(A) Precipitin test

(B) Complement fixation test

(C) Agglutination test

(D) Indirect fluorescent-antibody test

425. A woman had a high fever, hypotension, and a diffuse macular rash. When all cultures showed no bacterial growth, a diagnosis of toxic shock syndrome was made. Regarding the mechanism by which the toxin causes this disease, which one of the following is LEAST accurate?

(A) The toxin is not processed within the macrophage.

(B) The toxin binds to both the class II MHC protein and the T-cell receptor.

(C) The toxin activates many CD4-positive T cells, and large amounts of interleukins are released.

(D) The toxin has an A-B subunit structure—the B subunit binds to a receptor, and the A subunit enters the cells and activates them.

426. A patient with a central nervous system disorder is maintained on the drug methyldopa. Hemolytic anemia develops, which resolves shortly after the drug is withdrawn. This is MOST probably an example of:

(A) Atopic hypersensitivity

(B) Cytotoxic hypersensitivity

(C) Immune-complex hypersensitivity

(D) Cell-mediated hypersensitivity

427. Which one of the following substances is NOT released by activated helper T cells?

(A) Alpha interferon

(B) Gamma interferon

(C) Interleukin-2

(D) Interleukin-4

428. A delayed hypersensitivity reaction is characterized by:

(A) Edema without a cellular infiltrate

(B) An infiltrate composed of neutrophils

(C) An infiltrate composed of helper T cells and macrophages

(D) An infiltrate composed of eosinophils

429. Two dissimilar inbred strains of mice, A and B, are crossed to yield an F1 hybrid strain, AB. If a large dose of spleen cells from an adult A mouse is injected into an adult AB mouse, which one of the following is MOST likely to occur? (An explanation of the answer to this question is given on page 720.)

(A) The spleen cells will be destroyed.

(B) The spleen cells will survive and will have no effect in the recipient.

(C) The spleen cells will induce a graft-versus-host reaction in the recipient.

(D) The spleen cells will survive and induce tolerance of strain A grafts in the recipient.

430. This question is based on the same strains of mice described in the previous question. If adult AB spleen cells are injected into a newborn B mouse, which one of the following is MOST likely to occur? (An explanation of the answer to this question is given on page 720.)

(A) The spleen cells will be destroyed.

(B) The spleen cells will survive without any effect on the recipient.

(C) The spleen cells will induce a graft-versus-host reaction in the recipient.

(D) The spleen cells will survive and induce tolerance of strain A grafts in the recipient.

431. The minor histocompatibility antigens on cells:

(A) Are detected by reaction with antibodies and complement

(B) Are controlled by several genes in the major histocompatibility complex

(C) Are unimportant in human transplantation

(D) Induce reactions that can cumulatively lead to a strong rejection response

432. Which one of the following is NOT true of class I MHC antigens?

(A) They can be assayed by a cytotoxic test that uses antibody and complement.

(B) One of their two polypeptide chains is a beta-2-microglobulin.

(C) They are encoded by at least three gene loci in the major histocompatibility complex.

(D) They are found mainly on B cells, macrophages, and activated T cells.

433. An antigen found in relatively high concentration in the plasma of normal fetuses and a high proportion of patients with progressive carcinoma of the colon is:

(A) Viral antigen

(B) Carcinoembryonic antigen

(C) α-Fetoprotein

(D) Heterophil antigen

434. An antibody directed against the idiotypic determinants of a human IgG antibody would react with:

(A) The Fc part of the IgG

(B) An IgM antibody produced by the same plasma cell that produced the IgG

(C) All human kappa chains

(D) All human gamma chains

435. Which one of the following is NOT true of the gene segments that combine to make up a heavy chain gene?

(A) Many V region segments are available.

(B) Several J segments and several D segments are available.

(C) V, D, and J segments combine to encode the antigen-binding site.

(D) A V segment and a J segment are preselected by an antigen to make up the variable-region portion of the gene.

436. When immune complexes from the serum are deposited on glomerular basement membrane, damage to the membrane is caused mainly by:

(A) Gamma interferon

(B) Phagocytosis

(C) Cytotoxic T cells

(D) Enzymes released by polymorphonuclear cells

437. If an individual was genetically unable to make J chains, which immunoglobulin(s) would be affected?

(A) IgG

(B) IgM

(C) IgA

(D) IgG and IgM

(E) IgM and IgA

438. The antibody-binding site is formed primarily by:

(A) The constant regions of H and L chains

(B) The hypervariable regions of H and L chains

(C) The hypervariable regions of H chains

(D) The variable regions of H chains

(E) The variable regions of L chains

439. The class of immunoglobulin present in highest concentration in the blood of a human newborn is:

(A) IgG

(B) IgM

(C) IgA

(D) IgD

(E) IgE

440. Individuals of blood group type AB:

(A) Are Rh(D)-negative

(B) Are “universal recipients” of transfusions

(C) Have circulating anti-A and anti-B antibodies

(D) Have the same haplotype

441. Cytotoxic T cells induced by infection with virus A will kill target cells:

(A) From the same host infected with any virus

(B) Infected by virus A and identical at class I MHC loci of the cytotoxic T cells

(C) Infected by virus A and identical at class II MHC loci of the cytotoxic T cells

(D) Infected with a different virus and identical at class I MHC loci of the cytotoxic cells

(E) Infected with a different virus and identical at class II MHC loci of the cytotoxic cells

442. Antigen-presenting cells that activate helper T cells must express which one of the following on their surfaces?

(A) IgE

(B) Gamma interferon

(C) Class I MHC antigens

(D) Class II MHC antigens

443. Which one of the following does NOT contain C3b?

(A) Classic-pathway C5 convertase

(B) Alternative-pathway C5 convertase

(C) Classic-pathway C3 convertase

(D) Alternative-pathway C3 convertase

444. Which one of the following is NOT true regarding the alternative complement pathway?

(A) It can be triggered by infectious agents in absence of antibody.

(B) It does not require C1, C2, or C4.

(C) It cannot be initiated unless C3b fragments are already present.

(D) It has the same terminal sequence of events as the classic pathway.

445. In setting up a complement fixation test to detect antibody in the patient’s serum, the reactants should be added in what sequence? (Ag = antigen; C = complement; EA = antibody-coated indicator erythrocytes.)

(A) Ag + EA + C/wait/ + patient’s serum

(B) C + patient’s serum + EA/wait/ + Ag

(C) Ag + patient’s serum + EA/wait/ + C

(D) Ag + patient’s serum + C/wait/ + EA

446. Proteins from two samples of animal blood, A and B, were tested by the double-diffusion (Ouchterlony) test in agar against antibody to bovine albumin. Which sample(s) contain horse blood? (An explanation of the answer to this question is given on page 721.)

image

(A) Sample A

(B) Sample B

(C) Both samples

(D) Neither sample

447. Complement lyses cells by:

(A) Enzymatic digestion of the cell membrane

(B) Activation of adenylate cyclase

(C) Insertion of complement proteins into the cell membrane

(D) Inhibition of elongation factor-2

448. Graft and tumor rejection are mediated primarily by:

(A) Non–complement-fixing antibodies

(B) Phagocytic cells

(C) Helper T cells

(D) Cytotoxic T cells

449. Which one of the following properties of antibodies is NOT dependent on the structure of the heavy chain constant region?

(A) Ability to cross the placenta

(B) Isotype (class)

(C) Ability to fix complement

(D) Affinity for antigen

450. In which one of the following situations would a graft-versus-host reaction be MOST likely to occur? (Mouse strains A and B are highly inbred; AB is an F1 hybrid between strain A and strain B.)

(A) Newborn strain A spleen cells injected into a strain B adult

(B) X-irradiated adult strain A spleen cells injected into a strain B adult

(C) Adult strain A spleen cells injected into an x-irradiated strain AB adult

(D) Adult strain AB spleen cells injected into a strain A newborn

451. In a mixed-lymphocyte culture, lymphocytes from person X, who is homozygous for the HLA-Dw7 allele, are irradiated and then cultured with lymphocytes from person Z. It is found that DNA synthesis is NOT stimulated. The proper conclusion to be drawn is that:

(A) Person Z is homozygous for HLA-Dw7

(B) Person Z is homozygous or heterozygous for HLA-Dw7

(C) Person Z is heterozygous for HLA-Dw7

(D) Person Z does not carry the HLA-Dw7 allele

452. A patient skin-tested with purified protein derivative (PPD) to determine previous exposure to Mycobacterium tuberculosis develops induration at the skin test site 48 hours later. Histologically, the reaction site would MOST probably show:

(A) Eosinophils

(B) Neutrophils

(C) Helper T cells and macrophages

(D) B cells

453. Hemolytic disease of the newborn caused by Rh blood group incompatibility requires maternal antibody to enter the fetal bloodstream. Therefore, the mediator of this disease is:

(A) IgE antibody

(B) IgG antibody

(C) IgM antibody

(D) IgA antibody

454. An Rh-negative woman married to a heterozygous Rh-positive man has three children. The probability that all three of their children are Rh-positive is:

(A) 1:2

(B) 1:4

(C) 1:8

(D) Zero

455. Which one of the following statements BEST explains the relationship between inflammation of the heart (carditis) and infection with group A β-hemolytic streptococci?

(A) Streptococcal antigens induce antibodies cross-reactive with heart tissue.

(B) Streptococci are polyclonal activators of B cells.

(C) Streptococcal antigens bind to IgE on the surface of heart tissue and histamine is released.

(D) Streptococci are ingested by neutrophils that release proteases that damage heart tissue.

456. Your patient became ill 10 days ago with a viral disease. Laboratory examination reveals that the patient’s antibodies against this virus have a high ratio of IgM to IgG. What is your conclusion?

(A) It is unlikely that the patient has encountered this organism previously.

(B) The patient is predisposed to IgE-mediated hypersensitivity reactions.

(C) The information given is irrelevant to previous antigen exposure.

(D) It is likely that the patient has an autoimmune disease.

457. If you measure the ability of cytotoxic T cells from an HLA-B27 person to kill virus X–infected target cells, which one of the following statements is CORRECT?

(A) Any virus X–infected target cell will be killed.

(B) Only virus X–infected cells of HLA-B27 type will be killed.

(C) Any HLA-B27 cell will be killed.

(D) No HLA-B27 cell will be killed.

458. You have a patient who makes autoantibodies against his own red blood cells, leading to hemolysis. Which one of the following mechanisms is MOST likely to explain the hemolysis?

(A) Perforins from cytotoxic T cells lyse the red cells.

(B) Neutrophils release proteases that lyse the red cells.

(C) Interleukin-2 binds to its receptor on the red cells, which results in lysis of the red cells.

(D) Complement is activated, and membrane attack complexes lyse the red cells.

459. Your patient is a child who has no detectable T or B cells. This immunodeficiency is most probably the result of a defect in

(A) The thymus

(B) The membrane attack complex of complement

(C) T cell–B cell interaction

(D) Stem cells originating in the bone marrow

460. The role of the macrophage during an antibody response is to:

(A) Make antibody

(B) Lyse virus-infected target cells

(C) Activate cytotoxic T cells

(D) Process antigen and present it

461. The structural basis of blood group A and B antigen specificity is:

(A) A single terminal sugar residue

(B) A single terminal amino acid

(C) Multiple differences in the carbohydrate portion

(D) Multiple differences in the protein portion

462. Complement can enhance phagocytosis because of the presence on macrophages and neutrophils of receptors for:

(A) Factor D

(B) C3b

(C) C6

(D) C9

463. The main advantage of passive immunization over active immunization is that:

(A) It can be administered orally

(B) It provides antibody more rapidly

(C) Antibody persists for a longer period

(D) It contains primarily IgM

464. On January 15, a patient developed an illness suggestive of influenza, which lasted 1 week. On February 20, she had a similar illness. She had no influenza immunization during this period. Her hemagglutination inhibition titer to influenza A virus was 10 on January 18, 40 on January 30, and 320 on February 20. Which one of the following is the MOST appropriate interpretation?

(A) The patient was ill with influenza A on January 15.

(B) The patient was ill with influenza A on February 20.

(C) The patient was not infected with influenza virus.

(D) The patient has an autoimmune disease.

465. An individual who is heterozygous for Gm allotypes contains two allelic forms of IgG in serum, but individual lymphocytes produce only one of the two forms. This phenomenon, known as “allelic exclusion,” is consistent with:

(A) A rearrangement of a heavy chain gene on only one chromosome in a lymphocyte

(B) Rearrangements of heavy chain genes on both chromosomes in a lymphocyte

(C) A rearrangement of a light chain gene on only one chromosome in a lymphocyte

(D) Rearrangements of light chain genes on both chromosomes in a lymphocyte

466. Each of the following statements concerning class I MHC proteins is correct EXCEPT:

(A) They are cell surface proteins on virtually all cells.

(B) They are recognition elements for cytotoxic T cells.

(C) They are codominantly expressed.

(D) They are important in the skin test response to Mycobacterium tuberculosis.

467. Which one of the following is the BEST method of reducing the effect of graft-versus-host disease in a bone marrow recipient?

(A) Matching the complement components of donor and recipient

(B) Administering alpha interferon

(C) Removing mature T cells from the graft

(D) Removing pre–B cells from the graft

468. Regarding Th-1 and Th-2 cells, which one of the following is LEAST accurate?

(A) Th-1 cells produce gamma interferon and promote cell-mediated immunity.

(B) Th-2 cells produce interleukin-4 and-5 and promote antibody-mediated immunity.

(C) Both Th-1 and Th-2 cells have both CD3 and CD4 proteins on their outer cell membrane.

(D) Before naive Th cells differentiate into Th-1 or Th-2 cells, they are double-positives (i.e., they produce both gamma interferon and interleukin-4).

469. Each of the following statements concerning the variable regions of heavy chains and the variable regions of light chains in a given antibody molecule is correct EXCEPT:

(A) They have the same amino acid sequence.

(B) They define the specificity for antigen.

(C) They are encoded on different chromosomes.

(D) They contain the hypervariable regions.

470. Each of the following statements concerning class II MHC proteins is correct EXCEPT:

(A) They are found on the surface of both B and T cells.

(B) They have a high degree of polymorphism.

(C) They are involved in the presentation of antigen by macrophages.

(D) They have a binding site for CD4 proteins.

471. Which one of the following statements concerning immunoglobulin allotypes is CORRECT?

(A) Allotypes are found only on heavy chains.

(B) Allotypes are determined by class I MHC genes.

(C) Allotypes are confined to the variable regions.

(D) Allotypes are due to genetic polymorphism within a species.

472. Each of the following statements concerning immunologic tolerance is correct EXCEPT:

(A) Tolerance is not antigen-specific (i.e., paralysis of the immune cells results in a failure to produce a response against many antigens).

(B) Tolerance is more easily induced in T cells than in B cells.

(C) Tolerance is more easily induced in neonates than in adults.

(D) Tolerance is more easily induced by simple molecules than by complex ones.

473. Each of the following statements concerning a hybridoma cell is correct EXCEPT:

(A) The spleen cell component provides the ability to form antibody.

(B) The myeloma cell component provides the ability to grow indefinitely.

(C) The antibody produced by a hybridoma cell is IgM, because heavy chain switching does not occur.

(D) The antibody produced by a hybridoma cell is homogeneous (i.e., it is directed against a single epitope).

474. Each of the following statements concerning haptens is correct EXCEPT:

(A) A hapten can combine with (bind to) an antibody.

(B) A hapten cannot induce an antibody by itself; rather, it must be bound to a carrier protein to be able to induce antibody.

(C) In both penicillin-induced anaphylaxis and poison ivy, the allergens are haptens.

(D) Haptens must be processed by CD8+ cells to become immunogenic.

Answers (Questions 387–474)

387. (B)

388. (B)

389. (A)

390. (D)

391. (C)

392. (B)

393. (C)

394. (C)

395. (A)

396. (B)

397. (C)

398. (D)

399. (C)

400. (B)

401. (C)

402. (A)

403. (B)

404. (D)

405. (B)

406. (C)

407. (C)

408. (C)

409. (B)

410. (D)

411. (D)

412. (B)

413. (C)

414. (A)

415. (B)

416. (D)

417. (A)

418. (C)

419. (B)

420. (A)

421. (B)

422. (D)

423. (B)

424. (D)

425. (D)

426. (B)

427. (A)

428. (C)

429. (C)

430. (D)

431. (D)

432. (D)

433. (B)

434. (B)

435. (D)

436. (D)

437. (E)

438. (B)

439. (A)

440. (B)

441. (B)

442. (D)

443. (C)

444. (C)

445. (D)

446. (B)

447. (C)

448. (D)

449. (D)

450. (C)

451. (B)

452. (C)

453. (B)

454. (C)

455. (A)

456. (A)

457. (B)

458. (D)

459. (D)

460. (D)

461. (A)

462. (B)

463. (B)

464. (A)

465. (A)

466. (D)

467. (C)

468. (D)

469. (A)

470. (A)

471. (D)

472. (A)

473. (C)

474. (D)

DIRECTIONS (Questions 475–535): Select the ONE lettered option that is MOST closely associated with the numbered items. Each lettered option may be selected once, more than once, or not at all.

Questions 475–480

(A) T cells

(B) B cells

(C) Macrophages

(D) B cells and macrophages

(E) T cells, B cells, and macrophages

475. Major source of interleukin-1

476. Acted on by interleukin-1

477. Major source of interleukin-2

478. Express class I MHC markers

479. Express class II MHC markers

480. Express surface immunoglobulin

Questions 481–484

(A) Primary antibody response

(B) Secondary antibody response

481. Appears more quickly and persists longer

482. Relatively richer in IgG

483. Relatively richer in IgM

484. Typically takes 7 to 10 days for antibody to appear

Questions 485–488

(A) Blood group A

(B) Blood group O

(C) Blood groups A and O

(D) Blood group AB

485. People with this type have circulating anti-A antibodies

486. People with this type have circulating anti-B antibodies

487. People with this type are called “universal donors”

488. People with this type are called “universal recipients”

Questions 489–494

(A) Variable region of light chain

(B) Variable region of heavy chain

(C) Variable regions of light and heavy chains

(D) Constant region of heavy chain

(E) Constant regions of light and heavy chains

489. Determines immunoglobulin class

490. Determines allotypes

491. Determines idiotypes

492. Binding of IgG to macrophages

493. Fixation of complement by IgG

494. Antigen-binding site

Questions 495–498

The following double-immunodiffusion plate contains antibody prepared against whole human serum in the center well. Identify the contents of each peripheral well from the following list (each well to be used once). (An explanation of the answer to this question is given on page 721.)

image

495. Whole human serum

496. Human IgG

497. Baboon IgG

498. Human transferrin

Questions 499–501

(A) Immediate hypersensitivity

(B) Cytotoxic hypersensitivity

(C) Immune-complex hypersensitivity

(D) Delayed hypersensitivity

499. Irregular deposition of IgG along glomerular basement membrane

500. Involves mast cells and basophils

501. Involves macrophages and helper T cells

Questions 502–505

(A) IgM

(B) IgG

(C) IgA

(D) IgE

502. Crosses the placenta

503. Can contain a polypeptide chain not synthesized by a B lymphocyte

504. Found in the milk of lactating women

505. Binds firmly to mast cells and triggers anaphylaxis

Questions 506–509

(A) Agglutination

(B) Precipitin test

(C) Immunofluorescence

(D) Enzyme immunoassay

506. Concentration of IgG in serum

507. Surface IgM on cells in a bone marrow smear

508. Growth hormone in serum

509. Type A blood group antigen on erythrocytes

Questions 510–513

(A) IgA

(B) IgE

(C) IgG

(D) IgM

510. Present in highest concentration in serum

511. Present in highest concentration in secretions

512. Present in lowest concentration in serum

513. Contains 10 heavy and 10 light chains

Questions 514–517

In this double-diffusion (Ouchterlony) assay, the center well contains antibody against whole human serum. The peripheral (numbered) wells each contain one of the following proteins:

image

(A) Human serum albumin at low concentration

(B) Human serum albumin at high concentration

(C) Human serum transferrin

(D) Sheep serum albumin

514. Which protein is present in well No. 1?

515. Which protein is present in well No. 2?

516. Which protein is present in well No. 3?

517. Which protein is present in well No. 4? (An explanation of the answer to this question is given on page 721.)

Questions 518–521

(A) Class I MHC proteins

(B) Class II MHC proteins

518. Involved in the presentation of antigen to CD4-positive cells

519. Involved in the presentation of antigen to CD8-positive cells

520. Involved in antibody responses to T-dependent antigens

521. Involved in target cell recognition by cytotoxic T cells

Questions 522–525

(A) Fab fragment of IgG

(B) Fc fragment of IgG

522. Contains an antigen-combining site

523. Contains hypervariable regions

524. Contains a complement-binding site

525. Is crystallizable

Questions 526–530

(A) Severe combined immunodeficiency disease (SCID)

(B) X-linked hypogammaglobulinemia

(C) Thymic aplasia

(D) Chronic granulomatous disease

(E) Hereditary angioedema

526. Caused by a defect in the ability of neutrophils to kill microorganisms

527. Caused by a development defect that results in a profound loss of T cells

528. Caused by a deficiency in an inhibitor of the C1 component of complement

529. Caused by a marked deficiency of B cells

530. Caused by a virtual absence of both B and T cells

Questions 531–535

(A) Systemic lupus erythematosus

(B) Rheumatoid arthritis

(C) Rheumatic fever

(D) Graves’ disease

(E) Myasthenia gravis

531. Associated with antibody to the thyroid-stimulating hormone (TSH) receptor

532. Associated with antibody to IgG

533. Associated with antibody to the acetylcholine receptor

534. Associated with antibody to DNA

535. Associated with antibody to streptococci

Answers (Questions 475–535)

475. (C)

476. (A)

477. (A)

478. (E)

479. (D)

480. (B)

481. (B)

482. (B)

483. (A)

484. (A)

485. (B)

486. (C)

487. (B)

488. (D)

489. (D)

490. (E)

491. (C)

492. (D)

493. (D)

494. (C)

495. (D)

496. (C)

497. (A)

498. (B)

499. (C)

500. (A)

501. (D)

502. (B)

503. (C)

504. (C)

505. (D)

506. (D)

507. (C)

508. (D)

509. (A)

510. (C)

511. (A)

512. (B)

513. (D)

514. (B)

515. (A)

516. (D)

517. (C)

518. (B)

519. (A)

520. (B)

521. (A)

522. (A)

523. (A)

524. (B)

525. (B)

526. (D)

527. (C)

528. (E)

529. (B)

530. (A)

531. (D)

532. (B)

533. (E)

534. (A)

535. (C)

Explanation of question 429: Spleen cells from the adult donor A will recognize the B antigen on the recipient’s cells as foreign. Spleen cells from the adult donor will contain mature CD4 and CD8 cells that will attack the recipient cells, causing a graft-versus-host reaction; therefore, answer C is correct. Because the recipient is tolerant to antigen A, the donor A spleen cells will not be destroyed; therefore, answer A is incorrect. Answer B is incorrect because although the donor cells will survive, they will have an effect on the recipient. Answer D is incorrect because the recipient is already tolerant to antigen A.

Explanation of question 430: Because the donor AB spleen cells will not see any foreign antigen in the recipient, no graft-versus-host reaction will occur; therefore, answer C is incorrect. The immune cells of the newborn mouse do not have the capability to kill the donor cells; therefore, answer A is incorrect. Answer D is more correct than answer B because the donor cells will survive and induce tolerance to antigen A in the newborn recipient.

Explanation of question 446: There is a line of identity between sample A and bovine albumin; therefore, sample A is bovine albumin. There is a line of identity between sample B and horse albumin; therefore, sample B is horse albumin. The answer to the question is therefore B. Note that there is a spur formed between the wells containing sample A and horse albumin and between the wells containing sample B and bovine albumin. The spur indicates partial identity between the two proteins. Partial identity means that there are epitopes shared between the two albumins but that, because they are from different species, there are epitopes unique to each protein, also. A spur is formed by the interaction of the subset of antibodies in the anti-bovine serum with the unique epitopes in bovine albumin. The other lines are formed by the interaction of the subset of antibodies in the anti-bovine serum with the epitopes shared by the two albumins.

Explanation of questions 495–498: The center well contains antibody against whole human serum; therefore, well D must contain whole human serum because there are multiple lines representing some of the many proteins in whole human serum. There is a line of identity between well C and a protein in whole human serum and a line of partial identity with that same protein and well A. This indicates that well C contains human IgG and well A contains baboon IgG. The concept of partial identity is explained above in the discussion of question 446. There is a line of nonidentity between wells B and C; therefore, well B contains human transferrin, a protein immunologically distinct from human IgG.

Explanation of questions 514–517: There is a line of identity between wells 1 and 2; therefore, they contain human serum albumin (HSA). Note that the line of immunoprecipitate is very close to well 2. This line would not form if well 2 contained the high concentration of HSA because it would be a zone of antigen excess and the line only forms in a zone of equivalence. Therefore, well 2 contains the low concentration and well 1 contains the high concentration of HSA. There is a line of partial identity between wells 2 and 3; therefore, well 3 contains sheep serum albumin (SSA). There is a line of nonidentity between wells 1 and 4 and wells 3 and 4; therefore, well 4 contains human transferrin, which is immunologically distinct from HSA and SSA.

EXTENDED MATCHING QUESTIONS

DIRECTIONS (Questions 536–593): Each set of matching questions in this section consists of a list of lettered options followed by several numbered items. For each numbered item, select the ONE lettered option that is MOST closely associated with it. Each lettered option may be selected once, more than once, or not at all.

(A) Capsule

(B) Periplasmic space

(C) Peptidoglycan

(D) Lipid A

(E) 30S ribosomal subunit

(F) G protein

(G) Pilus

(H) ADP-ribosylating enzyme

(I) Mesosome

(J) Flagellum

(K) Transposon

536. Is the site of action of lysozyme

537. Mediates adherence of bacteria to mucous membranes

538. Is the toxic component of endotoxin

(A) Skin

(B) Colon

(C) Nose

(D) Stomach

(E) Vagina

(F) Mouth

(G) Outer third of urethra

(H) Gingival crevice

(I) Pharynx

539. Anatomic location where Bacteroides fragilis is most commonly found

540. Anatomic location where Actinomyces israelii is most commonly found

(A) Toxic shock syndrome toxin

(B) Tetanus toxin

(C) Diphtheria toxin

(D) Cholera toxin

(E) Coagulase

(F) Botulinum toxin

(G) Alpha toxin of C. perfringens

(H) M protein

(I) Endotoxin

(J) Verotoxin

541. Blocks release of acetylcholine

542. Its lipid component causes fever and shock by inducing tumor necrosis factor (TNF)

543. Causes fever and shock by binding to the T-cell receptor

544. Inhibits protein synthesis by ADP-ribosylation of elongation factor-2

545. Increases cyclic AMP by ADP-ribosylation of a G protein

(A) Ampicillin

(B) Nafcillin

(C) Clindamycin

(D) Gentamicin

(E) Tetracycline

(F) Amphotericin B

(G) Ciprofloxacin

(H) Rifampin

(I) Sulfonamide

(J) Erythromycin

546. Inhibits protein synthesis by blocking formation of the initiation complex so that no polysomes form

547. Inhibits DNA gyrase

548. Inhibits folic acid synthesis; analogue of para-aminobenzoic acid

549. Inhibits peptidoglycan synthesis; resistant to β-lactamase

550. Inhibits RNA polymerase

(A) Streptococcus pneumoniae

(B) Streptococcus pyogenes

(C) Haemophilus influenzae

(D) Salmonella typhi

(E) Staphylococcus aureus

(F) Enterococcus faecalis

(G) Clostridium tetani

(H) Bordetella pertussis

(I) Escherichia coli

(J) Streptococcus agalactiae

(K) Staphylococcus epidermidis

(L) Streptococcus mutans

551. The vaccine contains a single serotype of a capsular polysaccharide coupled to a protein carrier

552. Immunogen in the vaccine is a toxoid

553. Causes acute glomerulonephritis; is β-hemolytic

554. Causes urinary tract infections; grows in 6.5% NaCl

555. Causes neonatal meningitis; is bacitracin-resistant

556. Causes meningitis in adults; is α-hemolytic and optochin-sensitive

557. Causes food poisoning; is coagulase-positive

(A) Escherichia coli

(B) Shigella sonnei

(C) Salmonella typhi

(D) Salmonella enteritidis

(E) Proteus mirabilis

(F) Pseudomonas aeruginosa

(G) Vibrio cholerae

(H) Campylobacter jejuni

(I) Helicobacter pylori

(J) Bacteroides fragilis

558. Causes gastritis and peptic ulcer; produces urease

559. Causes bloody diarrhea; does not ferment lactose and does not produce H2S

560. Causes peritonitis; is an obligate anaerobe

561. Causes wound infections with blue-green pus; is oxidase-positive

562. Comma-shaped rod; causes high-volume watery diarrhea

(A) Legionella pneumophila

(B) Yersinia pestis

(C) Haemophilus influenzae

(D) Corynebacterium diphtheriae

(E) Pasteurella multocida

(F) Bordetella pertussis

(G) Brucella melitensis

(H) Listeria monocytogenes

(I) Clostridium perfringens

(J) Neisseria gonorrhoeae

563. Gram-positive spore-forming rod that causes myonecrosis

564. Gram-negative rod that is transmitted by cat bite

565. Gram-negative rod that causes cough and lymphocytosis

(A) Mycobacterium tuberculosis

(B) Borrelia burgdorferi

(C) Nocardia asteroides

(D) Treponema pallidum

(E) Coxiella burnetii

(F) Mycoplasma pneumoniae

(G) Mycobacterium leprae

(H) Chlamydia trachomatis

(I) Rickettsia rickettsii

(J) Leptospira interrogans

566. Spirochete that does not have an animal reservoir

567. Obligate intracellular parasite that forms elementary bodies

568. Respiratory pathogen without a cell wall

(A) Influenza virus

(B) Adenovirus

(C) Hepatitis A virus

(D) Hepatitis B virus

(E) Herpes simplex virus

(F) Measles virus

(G) Human immunodeficiency virus

(H) Rabies virus

(I) Rotavirus

569. Nonenveloped virus with single-stranded, positive-polarity RNA

570. Enveloped virus with two identical strands of positive-polarity RNA

571. Enveloped virus with double-stranded DNA and DNA polymerase in the virion

572. Enveloped virus with segmented, negative-polarity, single-stranded RNA

573. Nonenveloped virus with segmented double-stranded RNA

(A) Herpes simplex virus type 1

(B) Rabies virus

(C) Varicella-zoster virus

(D) Measles virus

(E) Epstein–Barr virus

(F) Influenza virus

(G) Rubella virus

(H) Herpes simplex virus type 2

(I) Mumps virus

(J) Cytomegalovirus

(K) Parainfluenza virus

(L) Respiratory syncytial virus

574. Leading cause of congenital malformations; no vaccine available

575. Causes a painful vesicular rash along the course of a thoracic nerve

576. Causes encephalitis; killed vaccine available

577. Causes pharyngitis, lymphadenopathy, and a positive heterophil test

578. Causes retinitis and pneumonia in patients deficient in helper T cells

579. Causes encephalitis, especially in the temporal lobe

580. Causes pneumonia primarily in infants; induces giant cells

581. Causes orchitis that can result in sterility

(A) Human papillomavirus

(B) Hepatitis A virus

(C) Rotavirus

(D) Adenovirus

(E) Hepatitis delta virus (HDV)

(F) Parvovirus B19

(G) Human immunodeficiency virus

(H) Hepatitis B virus

(I) Sin Nombre virus (Hantavirus)

(J) Human T-cell lymphotropic virus

(K) Prion

(L) Hepatitis C virus

582. Most important cause of diarrhea in infants

583. A vaccine containing purified viral protein is available

584. Defective virus with an RNA genome

(A) Coccidioides immitis

(B) Cryptococcus neoformans

(C) Blastomyces dermatitidis

(D) Sporothrix schenckii

(E) Aspergillus fumigatus

(F) Candida albicans

(G) Histoplasma capsulatum

(H) Mucor species

(I) Microsporum canis

585. Dimorphic fungus that enters the body through puncture wounds in the skin

586. Nonseptate mold that invades tissue, especially in acidotic patients

587. Yeast that forms pseudohyphae when it invades tissue

(A) Giardia lamblia

(B) Plasmodium vivax

(C) Leishmania donovani

(D) Entamoeba histolytica

(E) Toxoplasma gondii

(F) Trypanosoma cruzi

(G) Pneumocystis carinii

(H) Plasmodium falciparum

(I) Naegleria fowleri

(J) Trichomonas vaginalis

588. Acquired while swimming; causes meningitis

589. Transmitted by reduviid bug and invades cardiac muscle

590. Amastigotes found within macrophages

(A) Echinococcus granulosus

(B) Clonorchis sinensis

(C) Strongyloides stercoralis

(D) Taenia solium

(E) Necator americanus

(F) Enterobius vermicularis

(G) Schistosoma haematobium

(H) Wuchereria bancrofti

(I) Trichinella spiralis

(J) Taenia saginata

591. Infection predisposes to bladder carcinoma

592. Ingestion of eggs can cause cysticercosis

593. Acquired by penetration of feet by larvae; causes anemia

Answers (Questions 536–593)

536. (C)

537. (G)

538. (D)

539. (B)

540. (H)

541. (F)

542. (I)

543. (A)

544. (C)

545. (D)

546. (D)

547. (G)

548. (I)

549. (B)

550. (H)

551. (C)

552. (G)

553. (B)

554. (F)

555. (J)

556. (A)

557. (E)

558. (I)

559. (B)

560. (J)

561. (F)

562. (G)

563. (I)

564. (E)

565. (F)

566. (D)

567. (H)

568. (F)

569. (C)

570. (G)

571. (D)

572. (A)

573. (I)

574. (J)

575. (C)

576. (B)

577. (E)

578. (J)

579. (A)

580. (L)

581. (I)

582. (C)

583. (H)

584. (E)

585. (D)

586. (H)

587. (F)

588. (I)

589. (F)

590. (C)

591. (G)

592. (D)

593. (E)

CLINICAL CASE QUESTIONS

DIRECTIONS (Questions 594–654): Select the ONE lettered answer that is BEST in each question.

CASE 1. Your patient is a 20-year-old woman with the sudden onset of fever to 104°F and a severe headache. Physical examination reveals nuchal rigidity. You suspect meningitis and do a spinal tap. Gram stain of the spinal fluid reveals many neutrophils and many gram-negative diplococci.

594. Of the following bacteria, which one is MOST likely to be the cause?

(A) Haemophilus influenzae

(B) Neisseria meningitidis

(C) Streptococcus pneumoniae

(D) Pseudomonas aeruginosa

595. Additional history reveals that she has had several serious infections with this organism previously. On the basis of this, which one of the following is the MOST likely predisposing factor?

(A) She is HIV antibody positive.

(B) She is deficient in CD8-positive T cells.

(C) She is deficient in one of the late-acting complement components.

(D) She is deficient in antigen presentation by her macrophages.

CASE 2. Your patient is a 70-year-old man with a long history of smoking who now has a fever and a cough productive of greenish sputum. You suspect pneumonia, and a chest X-ray confirms your suspicion.

596. If a Gram stain of the sputum reveals very small gram-negative rods and there is no growth on a blood agar but colonies do grow on chocolate agar supplemented with NAD and heme, which one of the following bacteria is the MOST likely cause?

(A) Chlamydia pneumoniae

(B) Legionella pneumophila

(C) Mycoplasma pneumoniae

(D) Haemophilus influenzae

CASE 3. Your patient is a 50-year-old woman who returned yesterday from a vacation in Peru, where there is an epidemic of cholera. She now has multiple episodes of diarrhea.

597. Of the following, which one is MOST compatible with cholera?

(A) Watery diarrhea without blood, no polys in the stool, and growth of curved gram-negative rods in the blood culture

(B) Watery diarrhea without blood, no polys in the stool, and no organisms in the blood culture

(C) Bloody diarrhea, polys in the stool, and growth of curved gram-negative rods in the blood culture

(D) Bloody diarrhea, polys in the stool, and no organisms in the blood culture

CASE 4. Your patient is a 55-year-old man who is coughing up greenish blood-streaked sputum. For the past 2 weeks, he has had fever and night sweats. He thinks he has lost about 10 pounds. On physical examination, there are crackles in the apex of the right lung, and a chest X-ray shows a cavity in that location.

598. Of the following, which one is the LEAST likely finding?

(A) Gram stain of the sputum shows no predominant organism.

(B) Culture of the sputum on blood agar shows no predominant organism.

(C) Culture of the sputum on Löwenstein-Jensen medium shows tan colonies after incubation for 4 weeks.

(D) Rapid plasma reagin test reveals the causative organism.

CASE 5. Your patient is a 5-year-old girl with bloody diarrhea and no vomiting. There is no history of travel outside of San Francisco. Stool culture grows both lactose-positive and lactose-negative colonies on EMB agar.

599. Of the following organisms, which one is MOST likely to be the cause?

(A) Shigella sonnei

(B) Salmonella typhi

(C) Campylobacter jejuni

(D) Helicobacter pylori

CASE 6. Your patient is a 25-year-old woman with acute onset of pain in her left lower quadrant. On pelvic examination, there is a cervical exudate and tenderness in the left adnexa. You conclude that she has pelvic inflammatory disease (PID) and order laboratory tests.

600. Of the following, which one is the LEAST informative laboratory result?

(A) Gram stain of the cervical exudate shows gram-negative diplococci within polys.

(B) Culture of the cervical exudate on Thayer-Martin agar shows oxidase-positive colonies.

(C) Fluorescent-antibody test shows cytoplasmic inclusions.

(D) Complement fixation test shows a rise in antibody titer.

CASE 7. Your patient is a 22-year-old man with fever, fatigue, and a new diastolic murmur. You suspect endocarditis and do a blood culture.

601. Which of the following statements is LEAST accurate?

(A) If he had dental surgery recently, one of the most likely organisms to grow would be a viridans group streptococcus.

(B) If he is an intravenous drug user, one of the most likely organisms to grow would be Candida albicans.

(C) If he had colon surgery recently, one of the most likely organisms to grow would be Enterococcus faecalis.

(D) If he has a prosthetic aortic valve, one of the most likely organisms to grow would be Streptococcus agalactiae.

In fact, none of the above organisms grew in the blood culture. What did grow was a gram-positive coccus arranged in clusters. When sub-cultured on blood agar, the colonies were surrounded by a zone of clear hemolysis, and a coagulase test was positive.

602. In view of this, which one of the following is MOST accurate?

(A) He is probably an intravenous drug user.

(B) He probably lives on a farm and has had contact with pregnant sheep.

(C) He probably has a common sexually transmitted disease.

(D) He probably has been camping and was bitten by a tick.

CASE 8. Your patient is a 70-year-old woman who had a hysterectomy for carcinoma of the uterus 3 days ago. She has an indwelling urinary catheter in place and now has a fever to 39°C, and the urine in the collection bottle is cloudy. A Gram stain of the urine specimen shows many neutrophils and gram-positive cocci in chains. You also do a urine culture.

603. Which one of the following is the MOST likely set of findings on the urine culture?

(A) β-Hemolytic colonies that are bacitracin-sensitive

(B) α-Hemolytic colonies that are optochin-sensitive

(C) Nonhemolytic colonies that grow in 6.5% sodium chloride

(D) Nonhemolytic colonies that grow only anaerobically

CASE 9. Your patient is a 27-year-old woman who was treated with oral ampicillin for cellulitis caused by Streptococcus pyogenes. Several days later, she developed bloody diarrhea. You suspect that she may have pseudomembranous colitis.

604. Regarding the causative organism of pseudomembranous colitis, which one of the following is the MOST accurate?

(A) It is an anaerobic gram-positive rod that produces exotoxins.

(B) It is a comma-shaped gram-negative rod that grows best at 41°C.

(C) It is an obligate intracellular parasite that grows in cell culture but not on blood agar.

(D) It is a yeast that forms germ tubes when incubated in human serum at 37°C.

CASE 10. Your patient is a 10-year-old girl who has had pain in her left arm for the past 5 days. On physical examination, her temperature is 38°C, and there is tenderness of the humerus near her deltoid. On X-ray of the humerus, an area of raised periosteum and erosion of bone is seen. You do a blood culture.

605. Which one of the following is the MOST likely set of findings?

(A) Gram-negative rods that grow on EMB agar, forming purple colonies and a green sheen

(B) Gram-positive cocci that grow on blood agar, causing a clear zone of hemolysis and are coagulase-positive

(C) Gram-positive rods that grow only anaerobically and form a double zone of hemolysis on blood agar

(D) Gram-negative diplococci that grow on blood agar, are oxidase-positive, and ferment maltose

CASE 11. Your patient is a 30-year-old man who is HIV antibody positive and has a history of Pneumocystis pneumonia 2 years ago. He now has an ulcerating lesion on the side of his tongue. A Giemsa stain of the biopsy specimen reveals budding yeasts within macrophages. A culture of the specimen grows an organism that is a budding yeast at 37°C but produces hyphae at 25°C.

606. Of the following, which one is the MOST likely organism to cause this infection?

(A) Coccidioides immitis

(B) Aspergillus fumigatus

(C) Histoplasma capsulatum

(D) Cryptococcus neoformans

CASE 12. Your patient is a 10-year-old boy who is receiving chemotherapy for acute leukemia. He develops fever, headache, and a stiff neck, and you make a presumptive diagnosis of meningitis and do a lumbar puncture. A Gram stain reveals a small gram-positive rod, and culture of the spinal fluid grows a β-hemolytic colony on blood agar.

607. Regarding this organism, which one of the following is MOST accurate?

(A) It has more than 100 serologic types.

(B) It produces an exotoxin that inhibits elongation factor-2.

(C) It is commonly acquired by eating unpasteurized dairy products.

(D) There is a toxoid vaccine available against this organism.

CASE 13. Ms. Jones calls to say that she, her husband, and their child have had nausea and vomiting for the past hour or so. Also, they have had some non-bloody diarrhea. You ask when their last meal together was, and she says they had a picnic lunch in the park about 3 hours ago. They have no fever.

608. Which one of the following is the MOST likely finding?

(A) Gram stain of the leftover food would show many gram-positive cocci in clusters.

(B) Gram stain of the stool would show many gram-negative diplococci.

(C) KOH prep of the leftover food would show many budding yeasts.

(D) Acid-fast stain of the stool would show many acid-fast rods.

CASE 14. Your patient is a 9-year-old boy who was sent home from school because his teacher thought he was acting strangely. This morning, he had a seizure and was rushed to the hospital. On physical examination, his temperature is 40°C and he has no nuchal rigidity. A computed tomography (CT) scan is normal. A lumbar puncture is done, and the spinal fluid protein and glucose are normal. A Gram stain of the spinal fluid reveals no organisms and no polys. He is treated with various antibiotics but becomes comatose and dies 2 days later. The blood culture and spinal fluid culture grow no bacteria or fungi. On autopsy of the brain, eosinophilic inclusion bodies are seen in the cytoplasm of neurons.

609. Of the following, which one is the MOST likely cause?

(A) Prions

(B) JC virus

(C) Rabies virus

(D) Herpes simplex virus type 1

CASE 15. Your patient is a 20-year-old man who was in a fist fight and suffered a broken jaw and lost two teeth. Several weeks later, he developed an abscess at the site of the trauma that drained to the surface of the skin, and yellowish granules were seen in the pus.

610. Regarding this disease, which one of the following is MOST accurate?

(A) The causative organism is a gram-positive rod that forms long filaments.

(B) The causative organism is a comma-shaped gram-negative rod that produces an exotoxin which increases cyclic AMP.

(C) The causative organism cannot be seen in the Gram stain but can be seen in an acid-fast stain.

(D) A combination of gram-negative cocci and spirochetes cause this disease.

CASE 16. Your patient is a 25-year-old man who is HIV antibody positive and has a CD4 count of 120 cells (normal, 1000–1500). He has had a mild headache for the past week and vomited once yesterday. On physical examination, he has a temperature of 38°C and mild nuchal rigidity but no papilledema. The rest of the physical examination is negative.

611. Of the following, which one is the MOST likely to be found on examination of the spinal fluid?

(A) Lymphs and gram-positive cocci resembling Streptococcus pneumoniae

(B) Lymphs and budding yeasts resembling Cryptococcus neoformans

(C) Polys and anaerobic gram-negative rods resembling Bacteroides fragilis

(D) Polys and septate hyphae resembling Aspergillus fumigatus

CASE 17. Your patient is a 25-year-old woman with a sore throat since yesterday. On physical examination, her throat is red, but no exudate is seen. Two enlarged, tender cervical lymph nodes are palpable. Her temperature is 101°F. A throat culture reveals no β-hemolytic colonies. After receiving this result, you do another physical examination, which reveals an enlarged spleen. A heterophil antibody test finds that sheep red blood cells are agglutinated by the patient’s serum.

612. Which one of the following is the MOST likely cause of this disease?

(A) Streptococcus pyogenes

(B) Corynebacterium diphtheriae

(C) Epstein–Barr virus

(D) Influenza virus

CASE 18. Your patient is a 15-year-old boy with migratory polyarthritis, fever, and a new, loud cardiac murmur. You make a clinical diagnosis of rheumatic fever.

613. Which one of the following laboratory results is MOST likely to be found in this patient?

(A) A blood culture is positive for Streptococcus pyogenes at this time.

(B) A throat culture is positive for Streptococcus pyogenes at this time.

(C) A Gram stain of the joint fluid shows gram-positive cocci in chains at this time.

(D) An anti-streptolysin O assay is positive at this time.

614. Which one of the following modes of pathogenesis is MOST compatible with a diagnosis of rheumatic fever?

(A) Bacteria attach to joint and heart tissue via pili, invade, and cause inflammation.

(B) Bacteria secrete exotoxins that circulate via the blood to the joints and heart.

(C) Bacterial antigens induce antibodies that cross-react with joint and heart tissue.

(D) Bacterial endotoxin induces interleukin-1 and tumor necrosis factor, which cause inflammation in joint and heart tissue.

615. Which one of the following approaches is MOST likely to prevent endocarditis in patients with rheumatic fever?

(A) They should take the streptococcal polysaccharide vaccine.

(B) They should take penicillin if they have dental surgery.

(C) They should take the toxoid vaccine every 5 years.

(D) They should take rifampin if they have abdominal surgery.

CASE 19. Your patient is a 10-year-old girl who has leukemia and is receiving chemotherapy through an indwelling venous catheter. She now has a fever of 39°C but is otherwise asymptomatic. You do a blood culture, and the laboratory reports growth of Staphylococcus epidermidis.

616. Which one of the following results is LEAST likely to be found by the clinical laboratory?

(A) Gram-positive cocci in clusters were seen on Gram stain of the blood culture.

(B) Subculture of the blood culture onto blood agar revealed nonhemolytic colonies.

(C) A coagulase test on the colonies was negative.

(D) A catalase test on the colonies was negative.

CASE 20. Your patient is a 25-year-old woman with several purpuric areas indicative of bleeding into the skin. Her vital signs are as follows: temperature, 38°C; blood pressure, 70/40; pulse, 140; respiratory rate, 24. You think she has septic shock and do a blood culture.

617. Which one of the following organisms is LEAST likely to be the cause of her septic shock?

(A) Corynebacterium diphtheriae

(B) Neisseria meningitidis

(C) Clostridium perfringens

(D) Escherichia coli

618. Of the following mechanisms, which one is LEAST likely to be involved with the pathogenesis of her septic shock?

(A) Increased amount of interleukin-1

(B) Activation of the alternate pathway of complement

(C) Increased amount of tumor necrosis factor

(D) Increased amount of antigen–antibody complexes

CASE 21. Your patient is a 55-year-old man with severe cellulitis of the right leg, high fever, and a teeth-chattering chill. He is a fisherman who was working on his boat in the waters off the Texas coast yesterday.

619. Which one of the following organisms is MOST likely to be the cause of his disease?

(A) Yersinia pestis

(B) Vibrio vulnificus

(C) Pasteurella multocida

(D) Brucella melitensis

CASE 22. Your patient is a 30-year-old woman with facial nerve paralysis. She also has fever and headache but does not have a stiff neck. On physical examination, she has a circular, erythematous, macular rash on the back of her thigh. You suspect that she has Lyme disease.

620. Of the following tests, which one is the MOST appropriate to order to confirm a diagnosis of Lyme disease?

(A) Blood culture to grow the organism

(B) Stain for inclusion bodies within cells involved in the rash

(C) Test for serum antibody against the organism

(D) Dark field microscopy

CASE 23. Your patient is a 60-year-old man with confusion for 2 months. He has no history of fever or stiff neck. On physical examination, he was ataxic and his coordination was abnormal. A diagnosis of tertiary syphilis was made by the laboratory.

621. Of the following tests, which one is the MOST appropriate to make a diagnosis of tertiary syphilis?

(A) Spinal fluid culture to grow the organism

(B) Stain for inclusion bodies in the lymphocytes in the spinal fluid

(C) Test for antibody in the spinal fluid that reacts with cardiolipin

(D) ELISA for the antigen in the spinal fluid

CASE 24. Your patient is a 65-year-old man who had an adenocarcinoma of the pancreas that was surgically removed. Several blood transfusions were given, and he did well until 2 weeks later, when fever, vomiting, and diarrhea began. Blood and stool cultures were negative, and the tests for Clostridium difficile and hepatitis B surface antigen were negative. A liver biopsy revealed intranuclear inclusion bodies.

622. Of the following, which one is the MOST likely cause?

(A) Adenovirus

(B) Cytomegalovirus

(C) Hepatitis A virus

(D) Rotavirus

CASE 25. Your patient is a 3-year-old girl with fever and pain in her right ear. On physical examination, the drum is found to be perforated, and a bloody exudate is seen. A Gram stain of the exudate reveals gram-positive diplococci.

623. Of the following, which one is the MOST likely cause?

(A) Streptococcus pyogenes

(B) Staphylococcus aureus

(C) Corynebacterium diphtheriae

(D) Streptococcus pneumoniae

CASE 26. Your patient is a 70-year-old man with a fever of 40°C and a very painful cellulitis of the right buttock. The skin appears necrotic, and there are several fluid-filled bullae. Crepitus can be felt, indicating gas in the tissue. A Gram stain of the exudate reveals large gram-positive rods.

624. Of the following, which one is the MOST likely cause?

(A) Clostridium perfringens

(B) Bacillus anthracis

(C) Corynebacterium diphtheriae

(D) Actinomyces israelii

CASE 27. Your patient is a 45-year-old woman with a cadaveric renal transplant that is being rejected despite immunosuppressive therapy. She is now in renal failure with a blood pH of 7.32. This morning, she awoke with a pain near her right eye. On physical examination, her temperature is 38°C, and the skin near her eye is necrotic. A biopsy specimen of the lesion contains nonseptate hyphae invading the blood vessels.

625. Of the following, which one is the MOST likely cause?

(A) Histoplasma capsulatum

(B) Aspergillus fumigatus

(C) Cryptococcus neoformans

(D) Mucor species

CASE 28. Your patient is a 35-year-old man who is HIV antibody positive and has a CD4 count of 85 cells. He recently had a seizure, and a magnetic resonance imaging (MRI) scan indicates a lesion in the temporal lobe. A brain biopsy specimen reveals multinucleated giant cells with intranuclear inclusions.

626. Of the following, which one is the MOST likely cause?

(A) Herpes simplex virus type 1

(B) Parvovirus B19

(C) Coxsackie virus

(D) Western equine encephalitis virus

CASE 29. Your patient is a 40-year-old woman with a severe attack of diarrhea that began on the airplane while she was returning from a vacation in the Middle East. She had had multiple episodes of watery, nonbloody diarrhea and little vomiting. She is afebrile. A stool culture reveals only lactose-fermenting colonies on EMB agar.

627. Of the following, which one is the MOST likely cause?

(A) Shigella sonnei

(B) Helicobacter pylori

(C) Escherichia coli

(D) Pseudomonas aeruginosa

CASE 30. Your patient is a 20-year-old man with a sore throat for the past 3 days. On physical examination, his temperature is 38°C, the pharynx is red, and several tender submaxillary nodes are palpable.

628. Of the following, which one is the MOST likely organism to cause this infection?

(A) Streptococcus agalactiae (group B Streptococcus)

(B) Streptococcus sanguis (a viridans group Streptococcus)

(C) Parvovirus B19

(D) Epstein–Barr virus

You do a throat culture, and many small, translucent colonies that are β-hemolytic grow on blood agar. Gram stain of one of these colonies reveals gram-positive cocci in chains.

629. Of the following, which one is the MOST likely organism to cause this infection?

(A) Streptococcus pneumoniae

(B) Streptococcus pyogenes

(C) Streptococcus agalactiae (group B Streptococcus)

(D) Peptostreptococcus species

CASE 31. Your patient is a 55-year-old woman with a lymphoma who is receiving chemotherapy via intravenous catheter. She suddenly develops fever, shaking chills, and hypotension.

630. Of the following, which one is the LEAST likely organism to cause this infection?

(A) Streptococcus pneumoniae

(B) Klebsiella pneumoniae

(C) Mycoplasma pneumoniae

(D) Proteus mirabilis

631. If a blood culture drawn from the patient described in case 31 grows a gram-negative rod, which one of the following is the LEAST likely organism to cause this infection?

(A) Bordetella pertussis

(B) Escherichia coli

(C) Pseudomonas aeruginosa

(D) Serratia marcescens

632. Of the following virulence factors, which one is the MOST likely to cause the fever and hypotension seen in the patient described in case 31?

(A) Pilus

(B) Capsule

(C) Lecithinase

(D) Lipopolysaccharide

CASE 32. Your patient is a 30-year-old woman who was part of a tour group visiting a Central American country. The day before leaving, several members of the group developed fever, abdominal cramps, and bloody diarrhea.

633. Of the following, which one is the LEAST likely organism to cause this infection?

(A) Shigella dysenteriae

(B) Salmonella enteritidis

(C) Vibrio cholerae

(D) Campylobacter jejuni

A stool culture reveals no lactose-negative colonies on the EMB agar.

634. Which one of the following is the MOST likely organism to cause this infection?

(A) Shigella dysenteriae

(B) Salmonella enteritidis

(C) Vibrio cholerae

(D) Campylobacter jejuni

CASE 33. Your patient is a 78-year-old man who had an episode of acute urinary retention and had to be catheterized. He then underwent cystoscopy to determine the cause of the retention. Two days later, he developed fever and suprapubic pain. Urinalysis revealed 50 white blood cells and 10 red blood cells per high-power field. Culture of the urine revealed a thin film of bacterial growth over the entire blood agar plate, and the urease test was positive.

635. Which one of the following is the MOST likely organism to cause this infection?

(A) Escherichia coli

(B) Proteus mirabilis

(C) Streptococcus faecalis

(D) Branhamella (Moraxellacatarrhalis

CASE 34. Your patient is a 40-year-old man with a depigmented lesion on his chest that appeared about a month ago. The skin of the lesion is thickened and has lost sensation. He has lived most of his life in rural Louisiana.

636. Of the following tests, which one is the MOST appropriate to do to reveal the cause of this disease?

(A) Perform a biopsy of the lesion and do an acid-fast stain

(B) Culture on Sabouraud’s agar and look for germ tubes

(C) Culture on blood agar anaerobically and do a Gram stain

(D) Obtain serum for a Weil-Felix agglutination test

CASE 35. Your patient is a 28-year-old man with third-degree burns over a large area of his back and left leg. This morning, he spiked a fever to 40°C and had two teeth-chattering chills. A blood culture grows a gram-negative rod that is oxidase-positive and produces a blue-green pigment.

637. Of the following, which one is the MOST likely organism to cause this infection?

(A) Prevotella melaninogenica

(B) Pseudomonas aeruginosa

(C) Proteus mirabilis

(D) Haemophilus influenzae

CASE 36. Your patient is a 32-year-old moving-van driver who lives in St. Louis. He arrived in San Francisco about 10 days ago after picking up furniture in Little Rock, Dallas, Albuquerque, and Phoenix. He now has a persistent cough and fever to 101°F, and he feels poorly. On physical examination, crackles are heard in the left lower lobe, and chest X-ray reveals an infiltrate in that area.

638. Of the following, which one is the LEAST accurate statement?

(A) He probably has spherules containing endospores in his lung.

(B) If dissemination to the bone occurs, this indicates a failure of his cell-mediated immunity.

(C) He probably acquired this disease by inhaling arthrospores.

(D) The causative organism of this disease exists as a yeast in the soil.

CASE 37. Your patient is a 25-year-old man with an ulcerated lesion on his penis that is not painful. You suspect that it may be a chancre.

639. Which one of the following tests is the MOST appropriate to do with the material from the lesion?

(A) Dark field microscopy

(B) Gram stain

(C) Acid-fast stain

(D) Culture on Thayer-Martin agar

640. Which one of the following tests is the MOST appropriate to do with the patient’s blood?

(A) Culture on blood agar

(B) Assay for antibodies that react with cardiolipin

(C) Assay for neutralizing antibody in human cell culture

(D) Heterophil antibody test

CASE 38. Your patient is a 6-year-old boy with papular and pustular skin lesions on his face. A serous, “honey-colored” fluid exudes from the lesions. You suspect impetigo. A Gram stain of the pus reveals many neutrophils and gram-positive cocci in chains.

641. If you cultured the pus on blood agar, which one of the following would you be MOST likely to see?

(A) Small β-hemolytic colonies containing bacteria that are bacitracin-sensitive

(B) Small α-hemolytic colonies containing bacteria that are resistant to optochin

(C) Large nonhemolytic colonies containing bacteria that are oxidase-positive

(D) Small nonhemolytic colonies containing bacteria that grow in 6.5% NaCl

CASE 39. Your patient is a 66-year-old woman being treated with chemotherapy for lymphoma. She develops fever to 38°C and a nonproductive cough. A chest X-ray reveals an infiltrate. You treat her empirically with an appropriate antibiotic. The following day, several vesicles appear on her chest.

642. Which one of the following viruses is the MOST likely cause of her disease?

(A) Measles virus

(B) Respiratory syncytial virus

(C) Varicella-zoster virus

(D) Rubella virus

CASE 40. Your patient is a 40-year-old woman with systemic lupus erythematosus who is being treated with high-dose prednisone during a flare of her disease. She develops a fever to 38°C and a cough productive of a small amount of greenish sputum. On physical examination, you hear coarse breath sounds in the left lower lobe. Chest X-ray reveals an infiltrate in that region. Gram stain of the sputum reveals long filaments of gram-positive rods.

643. Which one of the following organisms is the MOST likely cause of this disease?

(A) Mycobacterium kansasii

(B) Listeria monocytogenes

(C) Nocardia asteroides

(D) Mycoplasma pneumoniae

CASE 41. Your patient is a 10-year-old girl with acute leukemia who responded well to her first round of chemotherapy but not to the most recent one. In view of this, she had a bone marrow transplant and is on an immunosuppressive regimen. She is markedly granulocytopenic. Ten days after the transplant, she spikes a fever and coughs up bloody, purulent sputum. Chest X-ray shows pneumonia. A wet mount of the sputum shows septate hyphae with dichotomous (Y-shape) branching.

644. Which one of the following organisms is the MOST likely cause of this disease?

(A) Histoplasma capsulatum

(B) Aspergillus fumigatus

(C) Rhizopus nigricans

(D) Candida albicans

CASE 42. Your patient is a 30-year-old man with acute onset of fever to 40°C and a swollen, very tender right femoral node. His blood pressure is 90/50, and his pulse is 110. As you examine him, he has a teeth-chattering shaking chill. He returned from a camping trip in the Southern California desert 2 days ago.

645. Regarding this disease, which one of the following is MOST accurate?

(A) An aspirate of the node will reveal a small gram-negative rod with bipolar staining (appears like a “safety pin”).

(B) The organism was probably acquired by eating food contaminated with rodent excrement.

(C) The aspirate of the node should be cultured on Löwenstein-Jensen agar and an acid-fast stain performed.

(D) The organism causes disease primarily in people with impaired cell-mediated immunity.

CASE 43. Your patient is a 62-year-old woman with a history of carcinoma of the sigmoid colon that was removed 5 days ago. The surgery was complicated by the escape of bowel contents into the peritoneal cavity. She now has fever and pain in the perineum and left buttock. On physical examination, her temperature is 39°C, and myonecrosis with a foul-smelling discharge is found. A Gram stain of the exudate reveals gram-negative rods.

646. Of the following, which one is the MOST likely organism to cause this infection?

(A) Helicobacter pylori

(B) Bacteroides fragilis

(C) Salmonella typhi

(D) Vibrio parahaemolyticus

CASE 44. Your patient is an 18-year-old woman with a swollen left ankle. Two days ago, when the ankle began to swell, she thought she had twisted it playing soccer. However, today she has a fever to 38°C, and the ankle has become noticeably more swollen, warm, and red. Her other joints are asymptomatic. You aspirate fluid from the joint.

647. Using the joint fluid, which one of the following procedures is MOST likely to provide diagnostic information?

(A) Acid-fast stain and culture on Löwenstein-Jensen medium

(B) Gram stain and culture on chocolate agar

(C) Dark field microscopy and the VDRL test

(D) India ink stain and culture on Sabouraud’s agar

CASE 45. Your patient is a 6-year-old boy with a history of several episodes of pneumonia. A sweat test revealed an increased amount of chloride, indicating that he has cystic fibrosis. He now has a fever and is coughing up a thick, greenish sputum. A Gram stain of the sputum reveals gram-negative rods.

648. Of the following, which one is the MOST likely organism to cause this infection?

(A) Pseudomonas aeruginosa

(B) Haemophilus influenzae

(C) Legionella pneumophila

(D) Bordetella pertussis

CASE 46. Your patient is a 7-year-old boy with fever, two episodes of vomiting, and a severe headache that began this morning. He has no diarrhea. On physical examination, his temperature is 39°C, and nuchal rigidity is found. Examination of the spinal fluid revealed a white cell count of 800, of which 90% were lymphs, and a normal concentration of both protein and glucose. A Gram stain of the spinal fluid revealed no bacteria.

649. Of the following, which one is the MOST likely to cause this infection?

(A) Chlamydia trachomatis

(B) Mycobacterium avium-intracellulare

(C) Coxsackie virus

(D) Adenovirus

CASE 47. Your patient is a 22-year-old man who has been on a low-budget trip to India, where he ate many of the local foods. He has had a low-grade fever, anorexia, and mild abdominal pain for about a month. You suspect that he may have typhoid fever.

650. If he does have typhoid fever, which one of the following is the LEAST likely laboratory finding?

(A) Culture of the blood reveals gram-negative rods.

(B) Culture of the stool grows lactose-negative colonies in EMB agar.

(C) His serum contains antibodies that agglutinate Salmonella typhi.

(D) His serum contains antibodies that cause a positive Weil-Felix reaction.

CASE 48. Your patient is a 30-year-old man who is HIV antibody positive and has had two episodes of Pneumocystis pneumonia. He now complains of pain in his mouth and difficulty swallowing. On physical examination, you find several whitish plaques on his oropharyngeal mucosa.

651. Regarding the most likely causative organism, which one of the following statements is MOST accurate?

(A) It is a filamentous gram-positive rod that is part of the normal flora in the mouth.

(B) It is an anaerobic gram-negative rod that is part of the normal flora in the colon.

(C) It is a yeast that forms pseudohyphae when it invades tissue.

(D) It is a spirochete that grows only in cell culture.

CASE 49. Your patient is a 20-year-old woman with a rash that began this morning. She has been feeling feverish and anorexic for the past few days. On physical examination, there is a papular rash bilaterally over the chest, abdomen, and upper extremities including the hands. There are no vesicles and no petechiae. Cervical and axillary lymph nodes were palpable. Her temperature was 38°C. White blood count was 9000 with a normal differential.

652. Of the following organisms, which one is the MOST likely cause of her disease?

(A) Histoplasma capsulatum

(B) Coxiella burnetii

(C) Neisseria meningitidis

(D) Treponema pallidum

CASE 50. Your patient is a 10-year-old boy who fell, abraded the skin of his thigh, and developed cellulitis (i.e., the skin was red, hot, and tender). Several days later, the infection was treated with a topical antibiotic ointment, and the cellulitis gradually healed. However, 2 weeks later, he told his mother that his urine was cloudy and reddish, and she noted that his face was swollen. You suspect acute glomerulonephritis.

653. Regarding the causative organism, what is the MOST likely appearance of a Gram stain of the exudate from the skin infection?

(A) Gram-positive cocci in grapelike clusters

(B) Gram-positive cocci in chains

(C) Gram-positive diplococci

(D) Gram-negative diplococci

654. What is the pathogenesis of the cloudy urine and facial swelling?

(A) Toxin-mediated

(B) Direct invasion by the bacteria

(C) Immune complex–mediated

(D) Cell-mediated immunity (delayed hypersensitivity)

Answers (Questions 594–654)

594. (B)

595. (C)

596. (D)

597. (B)

598. (D)

599. (A)

600. (D)

601. (D)

602. (A)

603. (C)

604. (A)

605. (B)

606. (C)

607. (C)

608. (A)

609. (C)

610. (A)

611. (B)

612. (C)

613. (D)

614. (C)

615. (B)

616. (D)

617. (A)

618. (D)

619. (B)

620. (C)

621. (C)

622. (B)

623. (D)

624. (A)

625. (D)

626. (A)

627. (C)

628. (D)

629. (B)

630. (C)

631. (A)

632. (D)

633. (C)

634. (D)

635. (B)

636. (A)

637. (B)

638. (D)

639. (A)

640. (B)

641. (A)

642. (C)

643. (C)

644. (B)

645. (A)

646. (B)

647. (B)

648. (A)

649. (C)

650. (D)

651. (C)

652. (D)

653. (B)

654. (C)