ABMM key terms

The lowest concentration of an antimicrobial agent that visibly prevents growth of a standardized bacterial inoculum under defined test conditions, expressed in micrograms per milliliter and used to categorize isolates as susceptible, intermediate, or resistant.

A quantitative susceptibility method in which serial twofold dilutions of antimicrobials are prepared in liquid medium in multiwell trays and inoculated with a standardized organism suspension to determine the MIC.

A defined MIC or zone-diameter value used to classify an organism as susceptible, intermediate, or resistant, established from pharmacokinetic, pharmacodynamic, and clinical outcome data rather than laboratory convenience.

The lowest antimicrobial concentration that reduces the starting inoculum by at least 99.9 percent, determined by subculturing from clear MIC wells onto antimicrobial-free agar and counting surviving colonies.

A standardized agar-based method in which paper disks containing fixed antimicrobial amounts are placed on an inoculated plate; the resulting zone of inhibition diameter is measured and interpreted against published charts.

An enzyme produced by bacteria that hydrolyzes the beta-lactam ring of penicillins, cephalosporins, or carbapenems, inactivating the drug; detection guides therapy and infection control decisions.

A beta-lactamase that hydrolyzes penicillins and most cephalosporins including third-generation agents, typically inhibited by clavulanate, and frequently carried on transferable plasmids in Enterobacterales.

A beta-lactamase capable of hydrolyzing carbapenems such as meropenem or imipenem, often plasmid-mediated, and a major driver of multidrug-resistant gram-negative infections requiring rapid laboratory detection.

Resistance in staphylococci conferred by the mecA gene encoding an altered penicillin-binding protein (PBP2a) with low beta-lactam affinity, detected by cefoxitin disk testing or molecular methods.

A structured community of microorganisms attached to a surface and embedded in self-produced extracellular matrix, which reduces antimicrobial penetration and contributes to chronic and device-related infections.

Cell-density-dependent signaling in which bacteria release and detect small molecules to coordinate collective behaviors such as virulence factor expression, biofilm formation, and bioluminescence.

An identification technique that generates a protein mass spectrum from a colony and matches it to a reference library, providing species-level bacterial and yeast identification within minutes from culture.

A molecular method that amplifies and sequences conserved-yet-variable regions of the bacterial 16S rRNA gene to identify organisms, especially slow-growing or unculturable isolates, to genus or species level.

An enzymatic technique that exponentially amplifies a specific nucleic acid target through repeated cycles of denaturation, primer annealing, and extension, enabling detection of pathogens directly from specimens.

A PCR variant that monitors amplicon accumulation cycle by cycle using fluorescent reporters, allowing quantification of target load and faster turnaround than endpoint gel-based detection.

Determination of the complete DNA sequence of an organism, used for outbreak strain typing, resistance gene detection, and identification of transmission clusters at high discriminatory power.

A molecular typing method that separates large DNA fragments generated by rare-cutting restriction enzymes, historically used for bacterial strain comparison in outbreak investigations.

A differential staining procedure that divides bacteria into gram-positive (retaining crystal violet) and gram-negative (counterstained pink) groups based on cell wall structure, guiding early presumptive identification.

A test for the enzyme coagulase, which converts fibrinogen to fibrin; a positive result helps distinguish Staphylococcus aureus from most other staphylococcal species.

A colorimetric test detecting cytochrome c oxidase activity, used to separate oxidase-positive organisms such as Pseudomonas and Neisseria from oxidase-negative fermenters like Enterobacterales.

A heat-stable component of the gram-negative outer membrane that triggers fever and inflammation via toll-like receptor signaling; its detection is used in sterility and device safety testing.

Morphologic change in cultured cells caused by viral infection, such as rounding, syncytium formation, or detachment, observed by microscopy and used to detect and identify viruses.

A rapid viral culture technique in which specimen is centrifuged onto a cell monolayer in a vial, incubated briefly, and stained for viral antigen before full cytopathic effect develops.

A quantitative virologic method in which serial dilutions are inoculated onto cell monolayers and localized zones of lysis are counted to express infectious virus as plaque-forming units per milliliter.

A major genetic change in a virus produced by reassortment of segmented genomes between strains, yielding a novel surface antigen to which population immunity is limited and enabling pandemics.

Gradual accumulation of point mutations in viral surface protein genes that allows escape from existing antibody immunity and necessitates periodic vaccine strain updates.

A state in which a virus persists in host cells with minimal or no replication and can later reactivate to produce disease, as seen with herpesviruses.

The ability of certain fungi to grow as molds at ambient temperature and as yeasts at body temperature, a property that aids identification of agents such as Histoplasma and Sporothrix.

A rapid phenotypic test in which a yeast incubated in serum forms short tube-like projections; a positive result supports identification of Candida albicans.

The lowest antifungal concentration that kills at least 99.9 percent of the starting fungal inoculum, determined by subculture from MIC wells; not routinely performed in most clinical laboratories.

Microscopic inspection of stool, sometimes after concentration, to detect helminth eggs and larvae or protozoan trophozoites and cysts; sensitivity depends on parasite burden and collection timing.

A Romanowsky-type stain that colors chromatin and cytoplasm, used to examine blood films for malaria parasites and other blood-borne protozoa and to evaluate cell morphology.

Paired blood smears used for malaria diagnosis: the thick film concentrates parasites for sensitive detection, while the thin film preserves morphology for species identification and parasitemia quantification.

An infection acquired during the process of receiving care in a healthcare facility that was not present or incubating at admission, tracked through standardized surveillance definitions.

Cleaning of hands with soap and water or alcohol-based products at defined moments of patient care, the single most effective measure for preventing transmission of healthcare-associated pathogens.

Sets of transmission-based practices, including contact, droplet, and airborne categories, applied in addition to standard precautions to interrupt spread of specific pathogens in healthcare settings.

A cumulative summary of antimicrobial susceptibility results for a defined organism population over a period, used to guide empiric therapy and monitor resistance trends.

A program of scheduled testing of known organisms and reagents, documentation, and corrective action that verifies test performance remains within acceptable limits before patient results are reported.

External assessment in which a laboratory analyzes unknown specimens supplied by an accredited provider and compares results with peer laboratories to demonstrate ongoing competence.

A graded set of facility design, equipment, and work practice requirements, from BSL-1 to BSL-4, matched to the risk of the agents handled and the potential for laboratory-acquired infection.