Essential Microbiology for Dentistry. 5th ed.

Glossary of terms and abbreviations

16SRNA gene The small subunit of the bacterial and archaeal ribosome: The DNA sequence of this gene is the most commonly used taxonomic marker for microbial communities

abscess A localized collection of pus (see pus)

acidophile An organism that prefers acidic environments; such an organism is said to be acidophilic acquired immune deficiency syndrome (AIDS) The final stage of infection with the human immunodeficiency virus in which the patient has a low count of CD4+ T cells and suffers from opportunistic infections, opportunistic malignancies and/or encephalitis/ dementia

acquired immunity Immunity or resistance acquired at some point in an individual's lifetime active acquired immunity Immunity or resistance acquired as a result of the active production of antibodies and activated T cells

active immunization Stimulation of the immune system by intentional vaccination with foreign antigens acute disease A disease having a sudden onset and short duration acute-phase proteins Proteins whose concentration rises rapidly in body fluids following tissue injury or infection and which reduce inflammatory tissue damage adaptive immunity The development of specifically activated B and/or T cells following exposure to antigen

adhesion molecule Cell surface molecule that enhances intercellular interactions

adjuvant A substance that enhances the immune response to an antigen

aerotolerant anaerobe An organism that can live in the presence of oxygen but grows best in an anaerobic environment (one that contains no oxygen) affinity maturation Introduction of point mutations into immunoglobulin V genes that increases the strength of binding of antibody to antigen

agammaglobulinaemia Absence of, or extremely low levels of, the gamma fraction of serum globulin; sometimes used to denote the absence of immunoglobulins

agglutination The clumping of particles (including cells and latex beads) in solution

agglutination test Laboratory procedure that results in agglutination, usually following reaction with antibodies and antigenic determinants on particles

AIDS See acquired immunodeficiency syndrome

allergen An antigen to which one may become allergic

allergy Immediate hypersensitivity reaction in susceptible persons caused by release of pharmacological mediators from mast cells and basophils following interaction of surface-bound immunoglobulin E with allergen

a1-antitrypsin An acute-phase protein that neutralizes proteases released by bacteria or damaged tissue

аβ T cells T lymphocytes bearing T cell receptors consisting of a and β chains

alternative pathway Complement activation independent of antibody, often induced by bacterial products such as endotoxin and lipopolysaccharide

amino acids The basic units or building blocks of proteins

anaerobe An organism that does not require oxygen for survival; can exist in the absence of oxygen

anamnestic response An immune response following exposure to an antigen to which the individual is already sensitized; also known as a secondary response or memory response

anaphylactic shock Severe immune reaction mediated by immunoglobulin E, which may be fatal owing to constriction of bronchial smooth muscles

anaphylatoxin Complement split products C3a, C4a and C5a that directly cause smooth- muscle contraction and mast cell degranulation

anaphylaxis An immediate, severe, sometimes fatal, systemic allergic reaction

anergy Non-responsiveness to antigen. T cells may become specifically anergic when exposed to antigen in the absence of activation signal 2

angioedema Collections of fluid (oedema) in the skin, mucous membrane or viscera due to overproduction of anaphylatoxins

angstrom A unit of length, equivalent to 0.1 nm; roughly the diameter of an atom

antagonism The killing, injury or inhibition of one microorganism by products of another

antibiotic A substance produced by a microorganism that inhibits or destroys other microorganisms

antibody Immunoglobulin (a glycoprotein) molecule produced by B lymphocytes in response to an antigen; binds specifically to the antigen that induced its secretion; often protective

antibody-dependent cell-mediated cytotoxicity Killing of antibody- coated target cells by polymorphs, monocyte/macrophages or natural killer cells that have surface receptors for the Fc portion of immunoglobulin G

anticodon The trinucleotide sequence that is complementary to a codon; found on a transfer RNA molecule

antigen Any molecule that can induce an immune response; sometimes called an immunogen antigen presentation Display of short peptides bound to major histocompatibility complex molecules on antigen-presenting cells for recognition by T cells antigen-presenting cells (APCs) Cells that are able to present peptides on major histocompatibility complex molecules to T cells and activate them

antigen processing Digestion of complex antigen molecules into short peptides, assembly of peptide-major histocompatibility complexes and transport of complexes to the cell surface of antigen-presenting cells

antigenic determinant The smallest part of an antigen capable of stimulating the production of antibodies or activating T cells (see also epitope)

antigenic disguise Binding of normal, non-immunogenic, self molecules to the surface of a parasite so that its foreignness is masked

antigenic drift Minor structural changes of viral antigens due to point mutations

antigenic modulation Loss of antigen from cell surfaces following binding of antibody

antigenic shift Exchange of large segments of genetic material between viruses resulting in major changes in antigenicity

antigenic variation Modification of the structure of pathogen antigens

anti-idiotype vaccine Antiantipathogen antibody with immunostimulating properties similar to those of the pathogen

anti-idiotypic antibody Antibody against V regions of antibodies, B cell or T cell receptors

antimicrobial agent A drug, disinfectant or other substance that kills microorganisms or suppresses their growth

antisepsis Prevention of infection by inhibiting the growth of pathogens

antiseptic An agent or substance capable of effecting antisepsis; usually refers to a chemical disinfectant that is safe to use on living tissues

antiserum Serum containing a particular antibody or antibodies; also called immune serum

antisialagogue Substance that prevents salivation

antitoxin An antibody produced in response to a toxin; often capable of neutralizing the toxin that stimulated its production

APC See antigen-presenting cell

API Analytical Profile Index—a commercially available system to speciate and identify different bacteria

apicectomy An operation in which the apex of a tooth is removed

apoptosis A form of programmed cell death in which products of cell disintegration are packaged as membrane-bound particles that are readily phagocytosed

approximal Surface between adjacent teeth

aseptic technique Measures taken to ensure that living pathogens are absent

asymptomatic disease A disease having no symptoms

asymptomatic infection The presence of a pathogen in or on the body, without any symptoms of disease

atrophy Shrinkage in size of an organ or tissue by reduction in size of its cells

attenuated live vaccine Live vaccine containing organism of reduced virulence due to culturing under unfavourable conditions

autochthonous population A characteristic member of the microbial community of a habitat

autoclave An apparatus used for sterilization by steam under pressure

autogenic succession Bacterial succession influenced by microbial factors; for example, the metabolism of pioneer species lowers the redox potential during plaque development; this allows obligate anaerobes to colonize

autoimmune disease A disease in which the body produces antibodies directed against its own tissues

autoimmunity Diseases caused by pathogenic immune reactions against self antigens

autoradiography Exposure of a gel or blot to radiographic film to identify the position of a radioactive probe

autotroph An organism that uses carbon dioxide as its sole carbon source

avirulent Not virulent

axial filament An organelle of motility possessed by spirochaetes

B7 Molecules (B7.1 and B7.2) present on 'professional' antigen-presenting cells that bind to CD28 (to signal for activation) or CTLA-4 (to signal for inactivation) on T cells

bacillus (pl. bacilli) A rod-shaped bacterium; also a member of the genus Bacillus (aerobic, Grampositive, spore-forming rods)

bacteraemia The presence of bacteria in the blood stream

bacteria (sing. bacterium) Primitive, unicellular, prokaryotic microorganisms

bacterial succession Pattern of development of a microbial community

bactericidal agent A chemical agent or drug that kills bacteria; a bactericide

bacteriocins Proteins produced by certain bacteria (those possessing bacteriocinogenic plasmids) that can kill other bacteria

bacteriome Constituent bacterial component of the microbiome

bacteriophage A virus that infects a bacterium; also known simply as a phage

bacteriostatic agent A chemical agent or drug that inhibits the growth of bacteria

bacteriuria The presence of bacteria in the urine

basophil Type of polymorphonuclear leukocyte with granules that stain with basic dyes

B cell See B lymphocyte

B cell receptor (BCR) Surface Ig molecules on B cells that recognize and bind antigens

bcl-2 An inhibitor of programmed cell death

β2-microglobulin A polypeptide associated with major histocompatibility complex I molecules

binary fission A method of reproduction whereby one cell divides to become two cells

B lymphocyte Bone marrow-derived lymphocyte responsible for production of antibodies

blotting Transfer of proteins on to nitrocellulose following electrophoresis

bone marrow Primary lymphoid organ, the site of production and development of blood cells

botulinum toxin The neurotoxin produced by Clostridium botulinum; causes botulism

candidiasis Infection with, or disease caused by, a yeast in the genus Candida (usually C. albicans); formerly called moniliasis; also called candidosis

candidosis See candidiasis (pl. candidoses or candidiases)

capnophile An organism that grows best in the presence of increased concentrations of carbon dioxide

capsid The external protein coat or covering of a virion

capsomeres The protein units that make up the capsid of some virions

capsule An organized layer of glycocalyx, firmly attached to the outer surface of the bacterial cell wall

cariogenic Dental caries-inducing (e.g., bacteria, carbohydrate-rich diets, etc.)

carrier An individual with an asymptomatic infection that can be transmitted to other susceptible individuals

CD28 Surface molecule on T cells that binds to B7 on 'professional' antigen- presenting cells to transmit T cell activation signal 2

CD3 A group of proteins associated with the T cell receptor that help transmit activation signals following engagement of T cell receptors by major histocompatibility complex- peptide

CD4 Surface molecule on a subset of T cells that binds to major histocompatibility complex II molecules during antigen recognition. The receptor for human immunodeficiency virus

CD40 Surface molecule on 'professional' antigen-presenting cells that binds to CD40L on T-helper cells to transmit B cell activation signal 2

CD40 ligand (CD40L) Molecule present on T-helper cells that binds to CD40 on 'professional' antigen- presenting cells and can transmit signal 2 for activation

CD45RA A molecule found on naive T-helper cells

CD45RO A molecule found on memory T-helper cells

CD8 Surface molecule on a subset of T cells that binds to major histocompatibility complex I molecules during antigen recognition

cell membrane The protoplasmic boundary of all cells; controls permeability and serves other important functions

cell wall The outermost rigid layer of the cell (bacterial, fungal and plant cells)

cellulitis Spreading infection of subcutaneous tissues

centriole Tubular structure thought to play a role in nuclear division (mitosis) in animal cells and the cells of lower plants

cervicitis Inflammation of the neck of the uterus, the cervix uteri

chemokine One of a family of low- molecular-weight cytokines involved in lymphocyte trafficking

chemotaxis Migration of cells, especially phagocytes, towards a high concentration of a chemotactic factor

chitin A polysaccharide found in fungal cell walls, but not found in the cell walls of other microorganisms

chromatin The genetic material of the nucleus; consisting of DNA and associated proteins; during mitotic division, the chromatin condenses and is seen as chromosomes

chromosome A condensed form of chromatin; the location of genes; bacterial cells usually contain only one chromosome, which divides to become two just prior to binary fission

chronic disease A disease of slow progress and long duration

cilia (sing. cilium) Thin, hair-like organelles of motility

cistron The smallest functional unit of heredity; a length of chromosomal DNA associated with a single biochemical function; a gene may consist of one or more cistrons; sometimes used synonymously with gene

clade A group of organisms descended from a common ancestor, corresponding to a single branch on the tree of life

classical pathway Activation of complement by antigen-antibody complexes

climax community Stable complex microbial community that develops by, and is the final product of, the process of bacterial succession

clonal selection The process whereby an antigen induces proliferation of a single antigen-specific lymphocyte to produce large numbers of identical antigen-reactive daughter cells

coaggregation The attachment of a cell to a pre-attached organism by specific molecular interactions

coagulase A bacterial enzyme that causes plasma to clot or coagulate

coccus (pl. cocci) A spherical bacterium

codon A sequence of three nucleotides in a strand of messenger RNA that provides the genetic information (code) for a certain amino acid to be incorporated into a growing protein chain

coenzyme A substance that enhances or is necessary for the action of an enzyme; several vitamins are coenzymes; a type of cofactor

collagenase A bacterial enzyme that causes the breakdown of collagen

colonization resistance The ability of the resident microflora to prevent colonization by exogenous species

colony-stimulating factor Cytokines that stimulate haematopoiesis

commensalism An interbacterial interaction beneficial to one population but with a neutral effect on the other

communicable disease A disease capable of being transmitted

community-acquired infection Any infection acquired outside a hospital setting

competition Rivalry among bacteria for growth-limiting nutrients

complement An enzyme cascade consisting of over 25 components (including C1-C9); involved in inflammation, chemotaxis, phagocytosis and lysis of microorganisms

conjugation As used in this book, the union of two bacterial cells, for the purpose of genetic transfer; not a reproductive process

convalescent carrier A person who no longer shows the signs of a particular infectious disease, but continues to harbour and transmit the pathogen during the convalescence period (e.g., hepatitis B)

co-stimulator molecule Molecule that stimulates second signals for activation

C-reactive protein An acute-phase protein that promotes phagocytosis of bacteria

C region Constant region of an antibody, B cell receptor or T cell receptor polypeptide

cross-reactivity Binding of antibody, B cell receptor or T cell receptor with antigen other than the one that induced activation CTLA-4 Like CD28, binds to B7, but unlike the former, induces T cell inactivation

cyst A fluid-filled pathological cavity lined by epithelium

cytokine Soluble hormone-like messenger of the immune system (e.g., lymphokines, monokines)

cytoplasm The portion of a cell's protoplasm that lies outside the nucleus of the cell

cytotoxic Detrimental or destructive to cells

cytotoxin Toxic substance that inhibits or destroys cells (e.g., verocytotoxin of Escherichia coli)

demineralization Dissolution of enamel or cementum by acid

dendritic cell A type of 'professional' antigen-presenting cell present in secondary lymphoid tissues that expresses high levels of major histocompatibility complex I and II molecules

dental caries Localized dissolution of the enamel or root surface by acid derived from the microbial degradation of dietary carbohydrates

dental plaque Tenacious deposit on the tooth surface comprising bacteria, their extracellular products and polymers of salivary origin

deoxyribonucleic acid (DNA) A macromolecule containing the genetic code in the form of genes

dermatophyte Fungal organism causing superficial mycosis of the skin, hair or nails

diplococci Cocci arranged in pairs

disinfect To destroy pathogens in or on any substance or to inhibit their growth and vital activity

disinfectant A chemical agent used to destroy pathogens or inhibit their growth; usually refers to a chemical agent used on inanimate material

disinfection A process that kills or removes pathogenic organisms in a material or an object, excluding bacterial spores so that they pose no threat of infection

diversity (D) gene Selectable V-region genes of B cell receptor H chains, T cell receptor β chains and T cell receptor δ chains, which contribute to the diversity of B and T cell repertoires

DNA See deoxyribonucleic acid

ecology The branch of biology concerned with interrelationships among living organisms; encompassing the relationships of organisms to each other, to the environment and to the entire energy balance within a given ecosystem

ecosystem An ecological system that includes all the organisms and the environment within which they occur naturally

empirical therapy Therapy (usually antibiotics) prescribed without the benefit of laboratory tests

encephalitis Inflammation or infection of the brain

encephalomyelitis Inflammation or infection of the brain and spinal cord

endemic disease A disease that is always present in a particular community or region

endogenous processing The processing of intracellular proteins, including those of intracellular pathogens, onto major histocompatibility complex I molecules for recognition by cytotoxic T cells

endoplasmic reticulum The network of cytoplasmic tubules and flattened sacs in a eukaryotic cell

endospore A resistant body formed within a bacterial cell

endotoxin The lipid portion of the lipopolysaccharide found in the cell walls of Gram-negative bacteria; intracellular toxin

enriched medium Culture medium that enables isolation of fastidious organisms from samples or specimens and growth in the laboratory

enterotoxin A bacterial toxin specific for cells of the intestinal mucosa

eosinophil Type of polymorphonuclear leukocyte with granules that stain with acidic dyes, such as eosin

epidemic disease A disease occurring in a higher than usual number of cases in a population during a given time interval

epidemiology The study of relationships between the various factors that determine the frequency and distribution of diseases

episome An extrachromosomal element (plasmid) that may either integrate into the host bacterium's chromosome or replicate and function stably when physically separated from the chromosome

epitope The portion of an antigen that binds to the V region of an antibody, B cell receptor or T cell receptor

erythrogenic toxin A bacterial toxin that produces redness, usually in the form of a rash

eukaryotic cell A cell containing a true nucleus; organisms having such cells are referred to as eukaryotes

exogenous processing Processing of endocytosed extracellular proteins onto major histocompatibility complex II molecules for recognition by T-helper cells

exotoxin A toxin that is released from the cell; an extracellular toxin (opposite of endotoxin)

exudate Any fluid (e.g., pus) that exudes (oozes) from tissue, often as a result of injury, infection or inflammation

fastidious bacterium A bacterium that is difficult to isolate or grow in the laboratory owing to its complex nutritional requirements

Fc receptors Cell surface molecules on phagocytes and natural killer cells that bind to antibody-coated target cells

fermentation An anaerobic biochemical pathway in which substances are broken down, and energy and reduced compounds are produced; oxygen does not participate in the process

fimbria (pl. fimbriae) Fine short, hairlike filaments that extend from the bacterial cell surface; synonymous with pili (see pili)

flagellum (pl. flagella) A whip-like organelle of motility

fomite An inanimate object or substance capable of absorbing and transmitting a pathogen (e.g., bed linen, towels)

fungicidal agent A chemical agent or drug that kills fungi; a fungicide

fungus (pl. fungi) Eukaryotic, nonphotosynthetic microorganism that is saprophytic or parasitic

GALT See gut-associated lymphoid tissue

yδ T cells T cells using у and δ instead of a and β T cell receptor genes. Probably important in defence against bacteria

gene A functional unit of heredity that occupies a specific space (locus) on a chromosome; capable of directing the formation of an enzyme or other protein

generalized infection An infection that has spread throughout the body; also known as a systemic infection

generation time The time required for a cell to split into two cells; also called the doubling time

genetic vaccines Pathogen-specific RNA or DNA segments capable of inducing pathogen protein expression and both humoural and cell-mediated immunity

genomics The study of genes and their functions

genotype The complete genetic constitution of an individual; all of that individual's genes

genus (pl. genera) The first name in binomial nomenclature; contains closely related species

germinal centre The site of B cell activation and differentiation in secondary lymphoid tissue

gingival crevice Protected habitat formed where the teeth rise out of the gum

gingival crevicular fluid Serum-like exudate bathing and flushing the gingival crevice. It has a considerable influence on the ecology of this region by introducing (1) nutrients for the microbial community, and (2) components of the immune system and other host defences

gingivitis Inflammation or infection of the gingiva (gums)

glycocalyx Extracellular material that may or may not be firmly attached to the outer surface of the cell wall (e.g., capsule, slime layers)

gnotobiotic animal Germ-free animal deliberately infected with a known bacterial population or microflora

gp120 A component of the envelope of human immunodeficiency virus, responsible for binding to CD4

gp41 A component of the envelope of human immunodeficiency virus, responsible for fusion with target cell membranes

Gram stain A differential staining procedure named for its developer, Hans Christian Gram, a Danish bacteriologist; differentiates bacteria into those that stain purple (Grampositive) and those that stain pink/ red (Gram-negative)

granulocyte A granular leukocyte; neutrophils, eosinophils and basophils are examples

granuloma Collection of macrophages, epithelioid cells, giant cells and fibroblasts formed in response to chronic immune stimulation, for example, following persistent infection of macrophages

granzymes Granular proteases found in cytotoxic T cells and natural killer cells

growth curve A graphic representation of the change in size of a bacterial population over a period of time; includes a lag phase, a log phase, a stationary phase and a death phase

gut-associated lymphoid tissue (GALT) Accumulations of secondary lymphoid tissue associated with the gastrointestinal tract

haematopoietic stem cell Multipotent progenitor of all types of blood cells

haemolysin A bacterial enzyme capable of lysing erythrocytes and releasing their haemoglobin

haemolysis Destruction of red blood cells (erythrocytes) in such a manner that haemoglobin is liberated into the surrounding environment

hapten A small, non-antigenic molecule that becomes antigenic when combined with a large molecule

HBV Hepatitis B virus; the aetiological agent of serum hepatitis

HCV Hepatitis C virus; the aetiological agent of hepatitis C

HDV Hepatitis D virus; the aetiological agent of hepatitis D or delta hepatitis

hepatitis Inflammation of the liver

heterotroph An organism that uses organic chemicals as a source of carbon; sometimes called an organotroph

HGV Hepatitis G virus; the aetiological agent of hepatitis G

HIV Human immunodeficiency virus; the aetiological agent of acquired immunodeficiency syndrome

HLA See human leukocyte antigen

hopanoids Sterol-like molecules present in bacterial plasma membranes

host The organism on or in which a parasite lives

human immunodeficiency virus (HIV) The virus that causes acquired immunodeficiency syndrome

human leukocyte antigen (HLA) Product of the major histocompatibility complex in humans

hyaluronic acid A gelatinous mucopolysaccharide that acts as an intracellular cement in body tissue

hyaluronidase A bacterial enzyme that breaks down hyaluronic acid; sometimes called diffusing or spreading factor, because it enables bacteria to invade deeper into the tissue

hybridoma Hybrid cell produced by fusing an antibody-producing cell with a myeloma cell; hybridomas are immortal and produce monoclonal antibody

hyperimmune globulin Preparation containing specific antibodies used to prevent disease after exposure to a pathogen

hyperplasia Increase in the size of an organ by increase in the number of cells

hypersensitivity A condition in which there is an exaggerated or inappropriate immune reaction that causes tissue destruction or inflammation

hypha (pl. hyphae) Long, branching, thread-like tubes containing the fungal cytoplasm and its organelles; intertwining structural units of moulds

hypogammaglobulinaemia Decreased quantity of the gamma fraction of serum globulin, including a decreased quantity of immunoglobulins

ICAM See intercellular adhesion molecule

idiotype Antibody, B cell receptor and T cell receptor V regions

IFN See interferon

IgA Immunoglobulin class with the major function of protecting mucosal surfaces against pathogens

Iga, Igβ Proteins associated with the B cell receptor that help transmit B cell activation signals

IgD Immunoglobulin class found on mature B cell surfaces

IgE Immunoglobulin class that protects against helminths and is responsible for symptoms of allergy

IgG Major antibody class of the secondary immune response

IgM Major antibody class of the primary immune response

IL See interleukin

immune complex Complex of antigen with antibody

immune deviation Suppression of an ongoing immune response by a switch from type 1 to type 2 or type 2 to type 1 cytokine production

immunocompetent Able to produce a normal immune response

immunocompromised The state of being susceptible to infection by virtue of impairment or malfunction of the immune system

immunodeficiency A state in which the immune system is deficient in a particular type of immune response

immunodiagnostic procedures Diagnostic test procedures that utilize the principles of immunology; used to detect either antigen or antibody in clinical specimens

immunoglobulin Proteins, consisting of two light polypeptide chains and two heavy chains that function as antibodies

immunological synapse The signalling complex formed between an antigen-presenting cell and a T cell

immunostimulating complex (ISCOM) Preparation of antigen combined with saponin, cholesterol and phosphatidylcholine that induces strong T and B cell immune responses

immunosuppression A condition in which individuals are unable to mount a normal immune response owing to suppression or depression of their immune system

inactivated vaccine Killed whole organisms, products of organisms or subunits of organisms that induce protective immune responses

inclusion body Distinctive structure frequently formed in the nucleus and/or cytoplasm of cells infected with certain viruses

indigenous microflora Microorganisms that live on and in the healthy body; also called indigenous microbiota, normal flora

infective endocarditis Infection of the lining of the heart (endocardium)

inflammation A pathological process comprising a dynamic complex of cytological and histological reactions induced by injury or abnormal stimulation by physical, chemical or biological agents

innate immunity The natural protective mechanisms present before contact with antigen

intercellular adhesion molecule (ICAM) Molecule that interacts at cell surfaces to promote cell-cell contact

interferon (IFN) A class of small, antiviral glycoproteins, produced by cells infected with an animal virus; cell-specific and species-specific, but not virus-specific. Interferons are mediators that increase resistance to viral infection: IFN-a is produced by leukocytes, IFN-β by fibroblasts and IFN-y by activated T cells and natural killer cells; IFN-y has numerous effects in modulating immune responses

interleukin (IL) A mediator involved in signalling between cells of the immune system

intravenous immunoglobulin Pooled antibodies from normal donors used to provide passive protection against infection in patients with antibody deficiencies

invariant chain A molecule that stabilizes 'empty' major histocompatibility complex II molecules, which can be replaced by antigenic peptides

in vitro In an artificial environment, such as a laboratory setting

in vivo In a living organism; used in reference to what occurs within a living organism

ISCOM See immunostimulating complex

isotype Immunoglobulin class, dependent on the type of heavy-chain C gene used

isotype switching The change from expression of a 5' immunoglobulin CH gene by a B cell to expression of a downstream CH gene

joining (J) gene Selectable V-region genes of B cell receptors and T cell receptors that contribute to the diversity of B and T cell repertoires

к (kappa) light chain One of two types of immunoglobulin light chain

lag phase That part of a bacterial growth curve during which multiplication of the organisms is very slow or scarcely appreciable; the first phase in a bacterial growth curve

λ (lambda) light chain One of two types of immunoglobulin light chain

latency Incorporation of viral genes into those of the host cell without overt production of virions

latent infection An asymptomatic infection capable of manifesting symptoms under particular circumstances or if activated

lecithin A name given to several types of phospholipids that are essential constituents of animal and plant cells

lecithinase A bacterial enzyme capable of breaking down lecithin

leukocidin A bacterial enzyme capable of destroying leukocytes

leukocyte function-associated antigen (LFA) Molecule that interacts at cell surfaces to promote cell-cell contact

lipopolysaccharide A macromolecule of combined lipid and polysaccharide, found in the cell walls of Gram-negative bacteria

log phase Logarithmic phase; a bacterial growth phase during which maximal multiplication is occurring by geometrical progression; plotting the logarithm (log) of the number of organisms against time produces a straight upward-pointing line; the second phase in a bacterial growth curve; also known as the exponential growth phase

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