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