ABMM cheat sheet

Gram stain reaction reflects peptidoglycan thickness: thick layer retains crystal violet (gram positive); thin layer with outer membrane decolorizes and takes safranin (gram negative).

Catalase converts hydrogen peroxide to water and oxygen; staphylococci are catalase positive, streptococci catalase negative.

Coagulase positivity separates Staphylococcus aureus from most other staphylococci; S. saprophyticus is novobiocin resistant.

Lancefield grouping is based on cell wall carbohydrate antigens; group A is S. pyogenes, group B is S. agalactiae, group D includes enterococci.

Beta-hemolysis is complete red cell lysis, alpha is partial greening, gamma is none; S. pyogenes is bacitracin sensitive, S. agalactiae is bacitracin resistant and hippurate positive.

Oxidase tests cytochrome c oxidase; positive for Neisseria, Pseudomonas, and Aeromonas, negative for Enterobacterales.

Enterobacterales are glucose-fermenting, oxidase-negative gram-negative rods; lactose fermentation separates E. coli and Klebsiella (positive) from Salmonella and Shigella (negative).

H2S production on TSI or XLD appears black; Salmonella is H2S positive, Shigella is H2S negative.

Spore-forming obligate anaerobes (Clostridium) and non-spore-forming anaerobes (Bacteroides, Prevotella) require anaerobic culture for identification.

Enveloped viruses are inactivated by lipid solvents (ether, chloroform) and are generally more fragile; non-enveloped viruses resist these and survive better on surfaces.

PCR detects viral nucleic acid and does not require viable virus; serology (IgM vs IgG) indicates recent versus past infection or vaccination.

Herpesviruses establish latency: HSV and VZV in sensory ganglia, EBV and CMV in B cells and monocytes/myeloid cells respectively.

Hepatitis B serology: HBsAg indicates infection, anti-HBs indicates immunity, anti-HBc IgM indicates acute infection, HBeAg indicates high replication.

Influenza A and B undergo antigenic drift (point mutations) and shift (reassortment, A only); shift can cause pandemics.

HIV is a retrovirus with reverse transcriptase; diagnosis uses combined antigen/antibody screening confirmed by nucleic acid testing or differentiation assay.

Respiratory syncytial virus causes bronchiolitis in infants; diagnosis by nucleic acid amplification or antigen testing of respiratory specimens.

Cell culture cytopathic effect, hemadsorption, and immunofluorescence are traditional virus identification methods; shell vial culture accelerates detection.

Fungi are eukaryotes with ergosterol in the membrane; antibacterial antibiotics do not affect them, and antifungal selectivity targets ergosterol or chitin.

Germ tube formation in serum at 37°C distinguishes Candida albicans/dubliniensis from other Candida species.

Aspergillus species show septate hyphae with acute-angle (45°) branching; Mucorales show broad, non-septate hyphae with right-angle branching.

Cryptococcus neoformans is encapsulated, urease positive, and detected by India ink or cryptococcal antigen; it reproduces by budding yeasts.

Dermatophytes (Trichophyton, Microsporum, Epidermophyton) digest keratin and cause tinea; KOH preparation shows septate hyphae in skin and hair.

Histoplasma capsulatum is a dimorphic fungus: mold at 25°C, yeast at 37°C; intracellular yeast forms in macrophages.

Candida species identification uses chromogenic media, germ tube, and assimilation tests; C. glabrata is intrinsically less susceptible to azoles.

Pneumocystis jirovecii is detected by direct fluorescent antibody or PCR on respiratory specimens; beta-D-glucan can support diagnosis.

Giemsa-stained thick and thin blood films detect malaria; thick film is more sensitive, thin film allows species identification and parasitemia quantification.

Plasmodium falciparum shows multiple ring forms, banana-shaped gametocytes, and high parasitemia; P. vivax and P. ovale show Schüffner's dots.

Rapid diagnostic tests for malaria detect HRP-2 (P. falciparum) or aldolase/pLDH; HRP-2 persists after treatment and can yield false positives.

Entamoeba histolytica trophozoites may contain ingested red cells; E. coli trophozoites do not; differentiate by morphology and antigen/PCR.

Giardia lamblia cysts and trophozoites are identified in stool; antigen immunoassay or PCR increases sensitivity.

Cryptosporidium and Cyclospora are detected by modified acid-fast staining or direct fluorescent antibody; they cause watery diarrhea.

Strongyloides stercoralis larvae may be found in stool or duodenal fluid; hyperinfection occurs in immunosuppressed patients.

Toxoplasma gondii serology (IgG/IgM) is used in pregnancy; IgM positivity requires confirmatory testing because of false positives.

MIC is the lowest antimicrobial concentration that inhibits visible growth; MBC is the lowest concentration that kills 99.9% of the inoculum.

Disk diffusion (Kirby-Bauer) zone diameters are interpreted using CLSI or EUCAST breakpoints; zone size inversely correlates with MIC.

Broth microdilution is the reference method for MIC determination; gradient diffusion (Etest) provides a stable gradient on a strip.

Beta-lactamase production is detected by nitrocefin; ESBLs are screened by reduced susceptibility to cefotaxime/ceftazidime and confirmed by clavulanate synergy.

MRSA is detected by cefoxitin disk or oxacillin MIC; mecA/mecC PCR or penicillin-binding protein 2a agglutination confirms.

Inducible clindamycin resistance in staphylococci and streptococci is detected by D-test (erythromycin-clindamycin disk approximation).

Vancomycin-resistant enterococci are defined by vancomycin MIC ≥32 µg/mL; vanA and vanB genotypes are common.

Carbapenemase production is screened by carbapenem MICs and confirmed by PCR or phenotypic inhibition tests; carbapenem-resistant Enterobacterales are a public health threat.

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

Proficiency testing (PT) is required for regulated analytes; unacceptable PT results trigger corrective action and may lead to sanctions.

Quality control rules: Westgard multirule (1-2s warning, 1-3s and 2-2s rejection) guide run acceptance decisions.

Method validation before clinical use includes accuracy, precision, analytical sensitivity/specificity, and reportable range.

Turnaround time, cost per test, and staffing ratios are key operational metrics; lean and six-sigma methods reduce waste.

Biosafety levels: BSL-2 for most clinical specimens, BSL-3 for Mycobacterium tuberculosis and highly pathogenic agents.

Chain of custody and specimen rejection criteria (unlabeled, leaked, or improperly transported specimens) protect result integrity.

Competency assessment of testing personnel is required initially, semiannually, and annually per CLIA personnel standards.

PCR specificity derives from primers; sensitivity depends on amplification efficiency and detection chemistry (e.g., TaqMan probes).

Real-time PCR quantifies target by cycle threshold (Ct); lower Ct indicates higher target concentration.

Multiplex panels detect multiple pathogens in one reaction; cross-reactivity and competitive inhibition must be validated.

Whole-genome sequencing supports outbreak typing and resistance gene detection; bioinformatics pipelines require validation.

MALDI-TOF mass spectrometry identifies bacteria and fungi by protein spectral fingerprint; it requires a pure isolate.

Next-generation sequencing of 16S rRNA genes identifies bacteria directly from specimens but does not distinguish viability.

Digital PCR provides absolute quantification without a standard curve and improves detection of low-abundance targets.

Contamination control in molecular labs uses unidirectional workflow, separate pre- and post-amplification areas, and negative controls.

Incidence measures new cases per population at risk over time; prevalence measures all existing cases at a point or period.

Attack rate = (new cases among exposed or population) × 100; it describes outbreak magnitude.

Sensitivity = TP/(TP+FN); specificity = TN/(TN+FP); predictive values depend on prevalence.

Standard precautions apply to all patients; transmission-based precautions add contact, droplet, or airborne measures based on route.

Hand hygiene is the single most effective infection prevention measure; alcohol-based rubs are preferred when hands are not visibly soiled.

Notifiable disease reporting is mandated by state and local health authorities; laboratories report confirmed and sometimes presumptive results.

Outbreak investigation steps: verify diagnosis, establish case definition, find cases, generate hypotheses, and implement control measures.

Healthcare-associated infection surveillance uses standardized definitions (e.g., NHSN) to calculate device-associated infection rates per 1,000 device-days.

Gram stain reaction reflects peptidoglycan thickness: thick layer retains crystal violet (gram positive); thin layer with outer membrane decolorizes and takes safranin (gram negative).

Catalase converts hydrogen peroxide to water and oxygen; staphylococci are catalase positive, streptococci catalase negative.

Coagulase positivity separates Staphylococcus aureus from most other staphylococci; S. saprophyticus is novobiocin resistant.

Lancefield grouping is based on cell wall carbohydrate antigens; group A is S. pyogenes, group B is S. agalactiae, group D includes enterococci.

Beta-hemolysis is complete red cell lysis, alpha is partial greening, gamma is none; S. pyogenes is bacitracin sensitive, S. agalactiae is bacitracin resistant and hippurate positive.

Oxidase tests cytochrome c oxidase; positive for Neisseria, Pseudomonas, and Aeromonas, negative for Enterobacterales.

Enterobacterales are glucose-fermenting, oxidase-negative gram-negative rods; lactose fermentation separates E. coli and Klebsiella (positive) from Salmonella and Shigella (negative).

H2S production on TSI or XLD appears black; Salmonella is H2S positive, Shigella is H2S negative.

Spore-forming obligate anaerobes (Clostridium) and non-spore-forming anaerobes (Bacteroides, Prevotella) require anaerobic culture for identification.

Enveloped viruses are inactivated by lipid solvents (ether, chloroform) and are generally more fragile; non-enveloped viruses resist these and survive better on surfaces.

PCR detects viral nucleic acid and does not require viable virus; serology (IgM vs IgG) indicates recent versus past infection or vaccination.

Herpesviruses establish latency: HSV and VZV in sensory ganglia, EBV and CMV in B cells and monocytes/myeloid cells respectively.

Hepatitis B serology: HBsAg indicates infection, anti-HBs indicates immunity, anti-HBc IgM indicates acute infection, HBeAg indicates high replication.

Influenza A and B undergo antigenic drift (point mutations) and shift (reassortment, A only); shift can cause pandemics.

HIV is a retrovirus with reverse transcriptase; diagnosis uses combined antigen/antibody screening confirmed by nucleic acid testing or differentiation assay.

Respiratory syncytial virus causes bronchiolitis in infants; diagnosis by nucleic acid amplification or antigen testing of respiratory specimens.

Cell culture cytopathic effect, hemadsorption, and immunofluorescence are traditional virus identification methods; shell vial culture accelerates detection.

Fungi are eukaryotes with ergosterol in the membrane; antibacterial antibiotics do not affect them, and antifungal selectivity targets ergosterol or chitin.

Germ tube formation in serum at 37°C distinguishes Candida albicans/dubliniensis from other Candida species.

Aspergillus species show septate hyphae with acute-angle (45°) branching; Mucorales show broad, non-septate hyphae with right-angle branching.

Cryptococcus neoformans is encapsulated, urease positive, and detected by India ink or cryptococcal antigen; it reproduces by budding yeasts.

Dermatophytes (Trichophyton, Microsporum, Epidermophyton) digest keratin and cause tinea; KOH preparation shows septate hyphae in skin and hair.

Histoplasma capsulatum is a dimorphic fungus: mold at 25°C, yeast at 37°C; intracellular yeast forms in macrophages.

Candida species identification uses chromogenic media, germ tube, and assimilation tests; C. glabrata is intrinsically less susceptible to azoles.

Pneumocystis jirovecii is detected by direct fluorescent antibody or PCR on respiratory specimens; beta-D-glucan can support diagnosis.

Giemsa-stained thick and thin blood films detect malaria; thick film is more sensitive, thin film allows species identification and parasitemia quantification.

Plasmodium falciparum shows multiple ring forms, banana-shaped gametocytes, and high parasitemia; P. vivax and P. ovale show Schüffner's dots.

Rapid diagnostic tests for malaria detect HRP-2 (P. falciparum) or aldolase/pLDH; HRP-2 persists after treatment and can yield false positives.

Entamoeba histolytica trophozoites may contain ingested red cells; E. coli trophozoites do not; differentiate by morphology and antigen/PCR.

Giardia lamblia cysts and trophozoites are identified in stool; antigen immunoassay or PCR increases sensitivity.

Cryptosporidium and Cyclospora are detected by modified acid-fast staining or direct fluorescent antibody; they cause watery diarrhea.

Strongyloides stercoralis larvae may be found in stool or duodenal fluid; hyperinfection occurs in immunosuppressed patients.

Toxoplasma gondii serology (IgG/IgM) is used in pregnancy; IgM positivity requires confirmatory testing because of false positives.

MIC is the lowest antimicrobial concentration that inhibits visible growth; MBC is the lowest concentration that kills 99.9% of the inoculum.

Disk diffusion (Kirby-Bauer) zone diameters are interpreted using CLSI or EUCAST breakpoints; zone size inversely correlates with MIC.

Broth microdilution is the reference method for MIC determination; gradient diffusion (Etest) provides a stable gradient on a strip.

Beta-lactamase production is detected by nitrocefin; ESBLs are screened by reduced susceptibility to cefotaxime/ceftazidime and confirmed by clavulanate synergy.

MRSA is detected by cefoxitin disk or oxacillin MIC; mecA/mecC PCR or penicillin-binding protein 2a agglutination confirms.

Inducible clindamycin resistance in staphylococci and streptococci is detected by D-test (erythromycin-clindamycin disk approximation).

Vancomycin-resistant enterococci are defined by vancomycin MIC ≥32 µg/mL; vanA and vanB genotypes are common.

Carbapenemase production is screened by carbapenem MICs and confirmed by PCR or phenotypic inhibition tests; carbapenem-resistant Enterobacterales are a public health threat.

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

Proficiency testing (PT) is required for regulated analytes; unacceptable PT results trigger corrective action and may lead to sanctions.

Quality control rules: Westgard multirule (1-2s warning, 1-3s and 2-2s rejection) guide run acceptance decisions.

Method validation before clinical use includes accuracy, precision, analytical sensitivity/specificity, and reportable range.

Turnaround time, cost per test, and staffing ratios are key operational metrics; lean and six-sigma methods reduce waste.

Biosafety levels: BSL-2 for most clinical specimens, BSL-3 for Mycobacterium tuberculosis and highly pathogenic agents.

Chain of custody and specimen rejection criteria (unlabeled, leaked, or improperly transported specimens) protect result integrity.

Competency assessment of testing personnel is required initially, semiannually, and annually per CLIA personnel standards.

PCR specificity derives from primers; sensitivity depends on amplification efficiency and detection chemistry (e.g., TaqMan probes).

Real-time PCR quantifies target by cycle threshold (Ct); lower Ct indicates higher target concentration.

Multiplex panels detect multiple pathogens in one reaction; cross-reactivity and competitive inhibition must be validated.

Whole-genome sequencing supports outbreak typing and resistance gene detection; bioinformatics pipelines require validation.

MALDI-TOF mass spectrometry identifies bacteria and fungi by protein spectral fingerprint; it requires a pure isolate.

Next-generation sequencing of 16S rRNA genes identifies bacteria directly from specimens but does not distinguish viability.

Digital PCR provides absolute quantification without a standard curve and improves detection of low-abundance targets.

Contamination control in molecular labs uses unidirectional workflow, separate pre- and post-amplification areas, and negative controls.

Incidence measures new cases per population at risk over time; prevalence measures all existing cases at a point or period.

Attack rate = (new cases among exposed or population) × 100; it describes outbreak magnitude.

Sensitivity = TP/(TP+FN); specificity = TN/(TN+FP); predictive values depend on prevalence.

Standard precautions apply to all patients; transmission-based precautions add contact, droplet, or airborne measures based on route.

Hand hygiene is the single most effective infection prevention measure; alcohol-based rubs are preferred when hands are not visibly soiled.

Notifiable disease reporting is mandated by state and local health authorities; laboratories report confirmed and sometimes presumptive results.

Outbreak investigation steps: verify diagnosis, establish case definition, find cases, generate hypotheses, and implement control measures.

Healthcare-associated infection surveillance uses standardized definitions (e.g., NHSN) to calculate device-associated infection rates per 1,000 device-days.