ABMM flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Coagulase test

Differentiates Staphylococcus aureus (positive) from most other staphylococci (negative). Rabbit plasma is inoculated; clot formation indicates coagulase enzyme converting fibrinogen to fibrin.

Beta-hemolysis

Complete lysis of red blood cells in agar, producing a clear halo around colonies. Characteristic of Streptococcus pyogenes and S. agalactiae, distinguishing them from alpha- and gamma-hemolytic species.

Oxidase test

Detects cytochrome c oxidase activity using a chromogenic reagent that turns purple when oxidized. Positive in Neisseria, Pseudomonas, and Aeromonas; negative in Enterobacterales.

TSI H2S reaction

Triple sugar iron agar showing black precipitate indicates hydrogen sulfide production. Salmonella is H2S positive; Shigella is H2S negative, aiding species differentiation.

Antigenic shift

Major change in influenza A surface antigens due to reassortment of gene segments between strains, producing novel hemagglutinin or neuraminidase. Can cause pandemics because population immunity is absent.

HBsAg

Hepatitis B surface antigen; its presence indicates current infection, either acute or chronic. Anti-HBs instead indicates immunity from vaccination or resolved infection.

Herpesvirus latency

Herpesviruses persist in specific cells after primary infection: HSV and VZV in sensory ganglia, EBV in B cells, CMV in myeloid cells. Reactivation occurs with immunosuppression.

Ct value

Cycle threshold in real-time PCR, the cycle at which fluorescence exceeds background. Lower Ct values indicate higher target nucleic acid concentration in the specimen.

Shell vial culture

Rapid viral culture method using centrifugation to enhance infectivity followed by immunofluorescent staining of early viral antigens, shortening detection time compared with conventional tube culture.

Germ tube test

Inoculation of yeast into serum at 37°C for 2-3 hours; formation of short parallel-sided projections identifies Candida albicans and C. dubliniensis.

Aspergillus morphology

Septate hyphae with acute-angle (45°) branching seen on microscopy. Contrasts with Mucorales, which show broad, non-septate hyphae with right-angle branching.

Cryptococcal antigen

Latex agglutination or lateral flow test detecting capsular polysaccharide of Cryptococcus neoformans in serum or cerebrospinal fluid. Highly sensitive for cryptococcal meningitis.

Dimorphic fungi

Fungi growing as molds at 25°C and yeasts at 37°C. Examples include Histoplasma capsulatum, Blastomyces dermatitidis, and Coccidioides immitis.

Thick blood film

Giemsa-stained drop of blood examined for malaria parasites; more sensitive than thin film for detecting low parasitemia but does not allow reliable species identification.

Plasmodium falciparum

Malaria species showing multiple ring forms, banana-shaped gametocytes, and high parasitemia. Causes severe malaria with cerebral and renal complications.

Strongyloides stercoralis

Intestinal nematode whose larvae may appear in stool. Autoinfection can cause hyperinfection in immunosuppressed patients, especially with corticosteroid use.

Giardia lamblia

Flagellated protozoan causing watery diarrhea. Cysts and trophozoites are identified in stool; antigen immunoassay or PCR improves sensitivity.

MIC definition

Minimum inhibitory concentration: the lowest antimicrobial concentration that prevents visible growth of a standardized inoculum under defined conditions; interpreted against CLSI or EUCAST breakpoints.

ESBL confirmation

Extended-spectrum beta-lactamase production is confirmed by clavulanate synergy: a ≥5 mm increase in zone diameter or ≥3 twofold reduction in MIC for cefotaxime or ceftazidime with clavulanate.

D-test

Disk approximation test placing erythromycin and clindamycin disks adjacent; blunting of the clindamycin zone indicates inducible clindamycin resistance in staphylococci or streptococci.

MRSA detection

Cefoxitin disk or oxacillin MIC screens for methicillin resistance; mecA/mecC PCR or penicillin-binding protein 2a agglutination provides confirmation.

Carbapenemase screening

Reduced carbapenem susceptibility prompts phenotypic inhibition tests (e.g., modified carbapenem inactivation) or molecular detection of genes such as KPC, NDM, and OXA-48.

CLIA complexity

Federal categorization of tests as waived, moderate, or high complexity; laboratories must hold a certificate matching the highest complexity of testing performed.

Westgard 1-3s rule

Quality control rejection rule: a single control result exceeding the mean by more than three standard deviations indicates random error and unacceptable run performance.

Proficiency testing

Required external evaluation in which unknown specimens are analyzed and results compared with peer laboratories; unacceptable performance triggers corrective action and possible sanctions.

MALDI-TOF identification

Mass spectrometry method identifying bacteria and fungi by protein spectral fingerprint compared with a reference library; requires a pure isolate for reliable results.

Digital PCR

Partitions a sample into thousands of reactions for absolute target quantification without a standard curve; improves detection of low-abundance targets.

Multiplex PCR

Amplification of multiple targets in one reaction using several primer sets; requires validation for cross-reactivity and competitive inhibition among targets.

Attack rate

Proportion of exposed persons who develop disease during an outbreak: (new cases among exposed ÷ exposed population) × 100. Describes outbreak magnitude.

Sensitivity formula

Sensitivity = true positives ÷ (true positives + false negatives). It is the probability that a test correctly identifies those who have the condition.

Airborne precautions

Transmission-based precautions for pathogens spread by small droplet nuclei (e.g., Mycobacterium tuberculosis, measles, varicella); require N95 respirator and negative-pressure room.

Standard precautions

Infection control practices applied to all patients regardless of diagnosis, including hand hygiene, gloves, gowns, and safe handling of sharps and body fluids.