ACVM Veterinary Microbiology key terms

The lowest concentration of an antimicrobial agent that visibly prevents growth of a standardized bacterial inoculum under defined laboratory conditions, expressed in micrograms per milliliter.

A defined MIC or zone-diameter threshold, set by a standards body, that classifies an isolate as susceptible, intermediate, or resistant to a given drug and species.

A quantitative susceptibility method in which serial twofold drug dilutions in liquid medium are inoculated in multiwell plates and growth is read to determine the MIC.

A susceptibility method in which antibiotic-impregnated disks are placed on an inoculated agar plate and the resulting zone of growth inhibition is measured and compared to interpretive charts.

An enzyme, typically plasmid-encoded, that hydrolyzes penicillins and most cephalosporins including third-generation agents, while remaining inhibited by clavulanate; detected by combination testing.

A beta-lactamase capable of hydrolyzing carbapenems such as meropenem or imipenem, often conferring resistance to nearly all beta-lactams and complicating treatment of gram-negative infections.

Movement of genetic material between organisms by conjugation, transformation, or transduction rather than inheritance, a major route by which antimicrobial resistance and virulence genes spread among bacteria.

Transfer of DNA between bacteria through direct cell-to-cell contact, typically via a conjugative plasmid or integrative conjugative element encoding a type IV secretion system.

A DNA segment such as a plasmid, transposon, integron, or integrative conjugative element that can relocate within or between genomes and frequently carries resistance or virulence determinants.

An in vitro method that uses thermostable polymerase and specific primers to amplify a target nucleic acid sequence through repeated cycles of denaturation, annealing, and extension.

A PCR variant in which fluorescent signal generated during each cycle is monitored, allowing quantification of target nucleic acid and often eliminating the need for post-amplification gel analysis.

The amplification cycle at which a real-time PCR fluorescence signal first exceeds a defined background level; lower values generally indicate a higher initial target concentration.

Determination of the complete DNA sequence of an organism, used for outbreak tracing, resistance gene detection, virulence profiling, and taxonomic identification at high resolution.

A typing method that compares the DNA sequences of several conserved housekeeping genes to assign isolates to sequence types, useful for population structure and epidemiological comparisons.

The application of computational tools to store, align, compare, and interpret biological sequence and genomic data, including assembly, annotation, and phylogenetic analysis.

A differential staining procedure that divides bacteria by cell wall structure: gram-positive cells retain crystal violet and appear purple, while gram-negative cells decolorize and counterstain pink.

A culture technique that uses a medium formulated to favor the growth of a target organism while suppressing competitors, thereby increasing its numbers before isolation on solid media.

A growth medium containing substances that inhibit the growth of certain organisms while permitting others, allowing the recovery of a specific group from a mixed sample.

A medium that contains indicators revealing biochemical differences among organisms growing on it, such as lactose fermentation or hydrogen sulfide production, aiding colony identification.

The propagation of bacteria in or on artificial media under controlled conditions, used to isolate, identify, quantify, and test the susceptibility of organisms from clinical specimens.

A cross-linked polymer of sugar chains and short peptides forming the rigid mesh of the bacterial cell wall, the target of beta-lactam antibiotics and lysozyme.

A molecule of the gram-negative outer membrane composed of lipid A, core polysaccharide, and O antigen; lipid A acts as an endotoxin that triggers inflammatory responses.

Heat-stable lipopolysaccharide released from gram-negative bacterial outer membranes that activates innate immune cells and can cause fever, shock, and disseminated intravascular coagulation.

A protein toxin actively secreted by bacteria that acts on specific host targets and is often highly potent, typified by diphtheria, tetanus, and cholera toxins.

A bacterial surface molecule such as a fimbria, pilus, or lectin that binds specific host receptors and mediates initial attachment and colonization of tissues.

A structured community of microorganisms embedded in a self-produced matrix attached to a surface, which resists host defenses and antimicrobials and contributes to chronic infections.

Cell-density-dependent regulation in which bacteria release and detect small signaling molecules to coordinate group behaviors such as virulence factor production and biofilm formation.

A needle-like protein apparatus used by many gram-negative pathogens to inject effector proteins directly into host cells, subverting signaling, cytoskeleton, and immune responses.

A family of germline-encoded pattern recognition receptors on innate immune cells that detect conserved microbial molecules and trigger inflammatory and antimicrobial responses.

A conserved molecular structure shared by groups of microbes, such as lipopolysaccharide, flagellin, or viral RNA, that is recognized by innate pattern recognition receptors.

Coating of a pathogen with antibody or complement fragments so that phagocytes can bind it through Fc or complement receptors, enhancing engulfment and killing.

Receptor-mediated engulfment of particles or microbes by cells such as neutrophils and macrophages into a vesicle that fuses with lysosomes for intracellular killing.

A cascade of plasma proteins that, when activated by microbes or antibodies, generates opsonins, chemoattractants, and membrane attack complexes that lyse target cells.

A short-lived, highly motile granulocyte that phagocytoses and kills microbes using reactive oxygen species, antimicrobial peptides, and neutrophil extracellular traps, and dominates acute inflammation.

A process in which an activated B cell changes the heavy-chain constant region of its antibody from IgM or IgD to IgG, IgA, or IgE while retaining antigen specificity.

Antibody transferred from dam to offspring, mainly as colostral IgG in ruminants and pigs and transplacental IgG plus milk IgA in others, providing temporary passive protection.

Gradual accumulation of point mutations in viral surface proteins that allows escape from existing neutralizing antibody and drives the need for updated vaccines.

Abrupt emergence of a virus with a novel surface antigen combination, typically through reassortment of segmented genomes or recombination, leaving populations with little pre-existing immunity.

Exchange of genome segments between two viruses with segmented genomes during coinfection, producing progeny with novel gene combinations and potentially altered host range or virulence.

An antibody that binds a viral or bacterial surface structure and blocks attachment, entry, or toxin activity, thereby reducing infectivity in vitro and often in vivo.

Observable morphological change in cultured cells caused by viral infection, such as rounding, fusion, or detachment, used as a diagnostic indicator in cell culture.

Maintenance and growth of living cells in vitro under controlled conditions, used to isolate viruses, propagate pathogens, and study host-pathogen interactions.

A quantitative method in which serial virus dilutions infect a cell monolayer, and localized zones of lysis or cytopathic change are counted to estimate infectious titer.

A fungus that grows as a mold in the environment or at ambient temperature and as a yeast or spherule in host tissue or at body temperature, characteristic of several systemic pathogens.

A unicellular fungal growth form that reproduces mainly by budding or fission and forms smooth, often pasty colonies on culture media.

A filamentous fungal growth form composed of branching hyphae that form fuzzy or powdery colonies; hyphal septation and pigmentation aid identification.

The principal sterol of fungal cell membranes, analogous to cholesterol in animals, and the target of polyene and azole antifungal drugs.