Biochemical tests, A to Z

148 tests

• Culture MediaA7 / A8 Agar for Genital MycoplasmasUreaplasma pattern: Very small brown to dark colonies on manganese-containing media from urease activity.
• Carbohydrate/Amide UtilizationAcetamide UtilizationGrowth with blue color (alkaline).
• Carbohydrate/Amide UtilizationAcetate UtilizationVisible growth with blue color from alkalinization.
• Microscopy/StainsAcid-Fast Smear (Ziehl-Neelsen / Kinyoun)Red or fuchsia acid-fast bacilli against a blue or green background.
• Growth RequirementsAerotolerance TestObligate anaerobe: Growth anaerobically with no aerobic growth.
• Colony MorphologyAgar Pitting or CorrosionColony appears embedded, pits the agar, corrodes the surface, or leaves a depression after removal.
• Enzyme/Spot TestsAlkaline PhosphataseMethod-specific color development after substrate hydrolysis.
• Presumptive IdentificationAnaerobe Special-Potency DisksExample B. fragilis group profile: Vancomycin resistant, kanamycin resistant, colistin resistant.
• Growth RequirementsAnaerobic Atmosphere SystemsValid anaerobic run: Indicator confirms anaerobiosis and anaerobic control grows.
• Culture MediaAnaerobic Blood AgarGrowth with interpretable morphology supports anaerobic workup.
• Specimen Collection/TransportAnaerobic Specimen Transport SystemsAcceptable handling: Deep specimen protected from oxygen and drying, with timely delivery.
• Amino Acid UtilizationArginine DihydrolasePurple or alkaline color after incubation compared with the control.
• Enzyme/HydrolysisArylsulfatase (14-Day)Method-specific color development after substrate hydrolysis.
• Selective/Differential MediaAshdown AgarPositive screen: Dry, wrinkled, violet-purple colonies in the correct clinical and geographic context.
• Selective/Differential MediaB. cepacia Selective AgarPositive screen: Growth of colonies with medium-specific color or morphology compatible with B. cepacia complex.
• Antimicrobial SusceptibilityBacitracin Susceptibility (A disk)Positive (Susceptible): Any zone of inhibition, typically >10 mm.
• Selective/Differential MediaBacteroides Bile Esculin (BBE) AgarBile resistant/esculin positive: Growth with darkening supports B. fragilis group patterns.
• Growth RequirementsBCYE L-Cysteine RequirementLegionella pattern: Growth on BCYE with L-cysteine and no growth on BCYE without L-cysteine.
• Differential/Selective MediaBile EsculinGrowth with dark brown/blackening of the agar slant (>50%).
• Spot TestsBile SolubilityColony disintegrates/lyses, leaving an intact or depressed area.
• Molecular/Direct DetectionBorrelia PCR on Selected SpecimensDetected: Borrelia nucleic acid present in the tested specimen.
• Safety/ReferralBrucella Safety Rule-OutRule-out trigger: Compatible culture, Gram stain, biochemical, and exposure pattern that requires escalation.
• Enzyme/Spot TestsButyrate DiskDevelopment of a blue color within 5 minutes.
• Hemolysis/Synergy TestsCAMP TestArrowhead-shaped zone of enhanced beta-hemolysis at the junction.
• Growth RequirementsCampylobacter Microaerophilic Growth and TemperatureThermotolerant enteric Campylobacter pattern: Growth at 42 C under microaerophilic conditions.
• Enzyme/Substrate HydrolysisCasein, Xanthine, and Tyrosine HydrolysisPositive for a substrate: Clearing or digestion around growth on that substrate.
• Enzyme/Spot TestsCatalase TestCopious, immediate oxygen bubbles.
• Interpretive PrincipleCell Wall-Deficient Bacteria RuleCell wall-deficient pattern: No reliable Gram stain morphology, no routine colony recovery, and intrinsic beta-lactam/glycopeptide resistance.
• Selective/Differential MediaCetrimide AgarGrowth with yellow-green to blue-green pigment.
• Immunochemical/MicroscopyChlamydia Direct Antigen DetectionSpecific intracellular staining or antigen signal with adequate cells.
• Molecular/Direct DetectionChlamydia trachomatis NAATDetected: C. trachomatis target detected.
• Selective/Differential MediaCIN AgarPositive screen: Small colonies with a deep red center and translucent border.
• Carbohydrate/Amide UtilizationCitrate UtilizationGrowth on the slant with (or without color change). Indicator shifts from green to blue.
• Enzyme/Clotting TestsCoagulase TestSlide positive: Macroscopic clumping in plasma drop. Tube positive: Visible fibrin clot.
• Antimicrobial SusceptibilityColistin / Polymyxin Resistance ScreenResistant screen: Growth despite polymyxin/colistin exposure, supporting intrinsically resistant groups in the right context.
• SerologyCoxiella burnetii Phase I / Phase II SerologyAcute pattern: Phase II IgG or IgM response predominates, especially with seroconversion or rising titer.
• Amino Acid DecarboxylationDecarboxylase Tests (Moeller)Alkaline (purple) color compared to the base control, with growth.
• Enzyme/Plate TestsDNA Hydrolysis (DNase Test Agar)Clearing (colorless halo) around growth as methyl green is released from degraded DNA.
• Microscopy/StainsDonovan Bodies Tissue SmearIntracellular Donovan bodies within macrophages.
• Enzyme/Plate TestsEgg Yolk LecithinaseOpaque white precipitate or zone around growth.
• Microscopy/StainsEhrlichia / Anaplasma Morulae SmearMorulae seen in monocytes or granulocytes in a compatible clinical syndrome.
• Immunologic/Toxin DetectionElek Toxigenicity TestVisible precipitin line of identity with the toxigenic control.
• Immunologic/Grouping TestsEnteric SerotypingVisible agglutination with a specific antiserum and valid controls.
• Differential MediaEsculin HydrolysisBlackened medium.
• Carbohydrate FermentationFermentation Media (Glucose/Lactose/Sucrose)Positive (acid): Medium turns yellow (if phenol red) or yellow (if purple broth). Gas may be present in Durham tube.
• Microscopy/StainsFlagella Stain (Wet Mount)Presence or absence of flagella; arrangements can be polar, peritrichous, lophotrichous, etc.
• Pigment/Colony TestsFlexirubin Pigment KOH TestYellow pigment changes to red, orange-red, or purple-red after KOH.
• Microscopy/StainsFluorochrome AFB StainBright yellow-green or orange fluorescent bacilli, often beaded.
• Safety/ReferralFrancisella Cysteine Requirement / Safety Rule-OutRule-out trigger: Compatible organism and exposure profile requiring escalation.
• Antimicrobial SusceptibilityFurazolidone SusceptibilitySusceptible: Zone of inhibition around disk.
• Enzyme/ProteolysisGelatin HydrolysisPartial or complete liquefaction of inoculated tube.
• Enzyme/ProteolysisGelatin Stab Brush GrowthPositive pattern: Fine lateral growth radiating from the stab line, often described as test-tube-brush growth.
• Temperature ToleranceGrowth at 42°CGood growth at both 35°C and 42°C.
• Temperature ToleranceGrowth at 44 CGood growth at 44 C.
• Growth RequirementsHaemophilus SatellitismSatellite colonies or markedly enhanced growth near the helper streak.
• Selective/Differential MediaHE / XLD Enteric Selective AgarsSalmonella screen: Nonfermenting colonies with black centers on H2S-producing media.
• Enzyme/HydrolysisHippurate HydrolysisDeep purple color.
• Enzyme/IMViCIndole ProductionPink to red ring after adding reagent.
• Enzyme/Spot TestsIndoxyl Acetate HydrolysisBlue or blue-green color development according to the method.
• Growth ResistanceKCN GrowthVisible growth or turbidity in KCN medium.
• Selective/Differential MediaLaked Blood Kanamycin Vancomycin (LKV) AgarGrowth on LKV supports vancomycin-resistant anaerobic Gram-negative rod groups such as many Prevotella/Bacteroides patterns.
• Immunologic/Grouping TestsLancefield GroupingVisible agglutination with a specific group reagent.
• Respiration/ReductionLead Acetate H2S DetectionBlackening of the lead acetate paper.
• SerologyLeptospira Microscopic Agglutination Test (MAT)Supportive: High titer or seroconversion in compatible illness.
• Molecular/CultureLeptospira PCR and CulturePCR detected: Leptospira target detected from appropriate specimen.
• Enzyme/Spot TestsLeucine Aminopeptidase (LAP)Red color develops within 1 minute after cinnamaldehyde.
• Differential MediaLitmus Milk MediumAcid: Pink color (lactose ferm).
• Enzyme/ProteolysisLoeffler Serum Slant DigestionVisible digestion, pitting, or depression of the serum surface.
• SerologyLyme Disease Two-Tier SerologyPositive two-tier result: Supports Lyme disease in compatible clinical context.
• Differential MediaLysine Iron Agar (LIA)K/K: Alkaline slant/alkaline butt (Lysine decarboxylation).
• Enzyme/Susceptibility TestsLysostaphin SusceptibilitySusceptible: Lysis, clearing, or inhibition depending on method.
• Growth ResistanceLysozyme Broth ResistanceResistant: Visible growth in lysozyme broth.
• Molecular/Antigen DetectionM. tuberculosis Complex NAATDetected: MTB complex nucleic acid present, with resistance marker result if included by the assay.
• Selective/Differential MediaMacConkey AgarLactose fermenter: Pink to red colonies, often with bile precipitate.
• Carbohydrate/Organic Acid UtilizationMalonate UtilizationMedium turns blue from alkalinization.
• Carbohydrate UtilizationMaltose OxidationOxidizer: Open tube turns yellow while the oil-overlaid tube remains green.
• Selective/Differential MediaMannitol Egg Yolk Polymyxin (MYP) AgarTypical B. cereus: pink to red colonies from mannitol-negative growth with surrounding egg-yolk precipitate.
• Fermentation/IMViCMethyl Red / Voges-Proskauer (MRVP)MR positive: Bright red color (stable mixed acid production).
• Enzyme/Spot TestsMicrodase (Modified Oxidase)Blue to purple-blue color within 2 minutes.
• Microscopy/StainsModified Acid-Fast StainRed to pink branching filaments, rods, or beaded forms against the counterstain.
• Selective/Differential MediaModified Tinsdale / Tellurite MediumPositive screen: Black or gray-black colonies with a brown-black halo on Tinsdale-type medium.
• Motility/FlagellaMotility Testing (Semisolid)Diffuse/hazy growth spreading away from the stab line.
• Molecular/Antigen DetectionMPT64 / MPB64 MTB Complex Antigen TestControl line plus test line supports MTB complex identification from culture.
• Carbohydrate FermentationMRS Broth (Gas from Glucose)Growth with gas bubble in Durham tube.
• Enzyme/FluorogenicMUG (4-Methylumbelliferyl-b-D-Glucuronide)Electric blue fluorescence.
• Enzyme/Spot TestsMycobacterial Arylsulfatase (3-Day)Pink to red color after the 3-day read supports rapid arylsulfatase activity.
• Culture MediaMycobacterial Culture MediaPositive culture: Growth of acid-fast colonies or positive liquid culture requiring confirmation.
• Enzyme/Spot TestsMycobacterial Niacin AccumulationColor reaction indicating niacin accumulation; classic M. tuberculosis is usually positive.
• Respiration/ReductionMycobacterial Nitrate ReductionRed color after reagents before zinc indicates nitrate reduction.
• Colony MorphologyMycoplasma / Ureaplasma Colony MorphologyFried-egg pattern: Dense central growth with lighter peripheral zone, supporting Mycoplasma-like colony morphology.
• Metabolic DifferentiationMycoplasma / Ureaplasma Metabolic DifferentiationGlucose use: Acid shift supports M. pneumoniae-like metabolism.
• Culture MediaMycoplasma / Ureaplasma Specialized CultureCompatible pH change, tiny colonies, or organism recovery on specialized media.
• Antimicrobial SusceptibilityMycoplasma / Ureaplasma Susceptibility PrinciplesIntrinsic resistance: Cell wall-active agents are inactive.
• Molecular/Direct DetectionMycoplasma genitalium NAAT and Resistance MarkersDetected: M. genitalium target present.
• Molecular/SerologyMycoplasma pneumoniae NAAT and SerologyNAAT detected: M. pneumoniae target detected from respiratory specimen.
• Specimen ProcessingNALC-NaOH Digestion and DecontaminationAcceptable processing: Specimen liquefied with reduced contaminating flora while preserving mycobacterial recovery.
• Carbohydrate UtilizationNeisseria Carbohydrate UtilizationN. gonorrhoeae pattern: Glucose positive; maltose, lactose, and sucrose negative.
• Respiration/ReductionNitrate ReductionColor after Reagents A/B: Positive for nitrite (NO3 -> NO2).
• Respiration/ReductionNitrite ReductionPositive for nitrite reduction (NO2 destroyed): No color change after A/B, gas in Durham tube often present.
• Antimicrobial SusceptibilityNitrocefin Beta-Lactamase TestNitrocefin changes from yellow to red or pink, indicating beta-lactamase activity.
• Antimicrobial SusceptibilityNovobiocin SusceptibilitySusceptible: Zone diameter above the laboratory cutoff.
• Antimicrobial SusceptibilityO/129 Vibriostatic Agent SusceptibilitySusceptible: Zone of inhibition around the O/129 disk.
• Safety/ReferralObligate Intracellular Agent Culture SafetyEscalation trigger: Compatible exposure, syndrome, or direct finding that requires nonroutine testing or reference workflow.
• Enzyme/CarbohydrateONPG (o-Nitrophenyl-B-D-Galactopyranoside)Yellow color (o-nitrophenol present).
• Antimicrobial SusceptibilityOptochin SusceptibilitySusceptible: Clear zone of inhibition around the disk according to disk size and laboratory criteria.
• Enzyme/Spot TestsOxidase Test (Kovac's)Dark purple color within 10 seconds.
• Carbohydrate UtilizationOxidation/Fermentation (OF) MediumFermenter: Both tubes yellow (acid).
• Microscopy/Colony TestsPenicillin Disk Cell ElongationPositive elongation: Cells near the disk become elongated rods or filamentous forms.
• Amino Acid DeaminationPhenylalanine Deaminase AgarGreen color on slant after ferric chloride.
• Differential InhibitionPNB and TCH Mycobacterial InhibitionPNB susceptible: Growth inhibited on PNB, supporting MTB complex in classic algorithms.
• Growth RequirementsPorphyrin / ALA TestRed-orange fluorescence or method-specific positive color, supporting hemin synthesis and X-factor independence.
• Growth RequirementsPRAS / Pre-Reduced Anaerobic MediaReduced medium: Indicator remains in the reduced color state and supports anaerobic growth.
• Pigment/Colony TestsPseudomonas Pigment ProductionPyocyanin positive: Blue-green diffusible pigment.
• Enzyme/Spot TestsPYR (L-Pyrrolidonyl Arylamidase)Bright red within 5 minutes (usually within 1 minute after reagent).
• Carbohydrate UtilizationPyruvate BrothIndicator changes from green to yellow.
• Selective/Differential MediaRegan-Lowe / Bordet-Gengou MediaPositive recovery: Small shiny pearl-like or mercury-drop colonies after appropriate incubation.
• Microscopy/StainsRelapsing Fever Borrelia Blood SmearExtracellular helical organisms compatible with Borrelia seen in blood smear.
• Hemolysis/Synergy TestsReverse CAMP TestEnhanced hemolysis at the junction near the S. aureus streak.
• SerologyRickettsial IFA SerologyConfirmed recent infection: Seroconversion or at least fourfold IgG titer rise between paired sera.
• Molecular/Direct DetectionRickettsial, Ehrlichial, and Anaplasmal PCRDetected: Compatible organism-group nucleic acid present.
• Identification/ClassificationRunyon Growth and Pigment ClassificationPhotochromogen: Pigment develops after light exposure.
• Growth CharacteristicsSalt Tolerance (6.5% NaCl)Visible turbidity with or without purple-to-yellow shift.
• Growth RequirementsSatellitism / Pyridoxal RequirementSatellite colonies or markedly enhanced growth near the helper streak, or improved growth on pyridoxal-supplemented medium.
• Selective/Differential MediaSelective Neisseria MediaPositive recovery: Compatible oxidase-positive colonies grow on selective medium.
• Growth RequirementsSodium Polyanethole Sulfonate (SPS) InhibitionInhibited: No growth or reduced growth in the presence of SPS compared with the control.
• Selective/Differential MediaSorbitol MacConkey (SMAC) AgarSorbitol fermenter: Pink colonies.
• Microscopy/StainsSpirochete Darkfield MicroscopyThin, actively motile helical organisms with compatible morphology.
• Histology/MicroscopySpirochete Silver and ImmunostainsThin dark or specifically stained spiral organisms in a compatible distribution.
• Enzyme/Spot TestsSpot Indole TestBlue-green color within ~20 seconds.
• Enzyme/Plate TestsStarch HydrolysisClear zone around growth after iodine is added.
• Spot TestsString TestMucoid string forms when the loop is lifted.
• Enzyme/Spot TestsSuperoxol TestStrong positive: Immediate, profuse bubbling supporting N. gonorrhoeae in the correct context.
• SerologySyphilis Nontreponemal Tests (RPR / VDRL)Reactive: Flocculation or agglutination reported with titer when quantified.
• Diagnostic AlgorithmSyphilis Traditional and Reverse AlgorithmsConcordant reactive: Supports syphilis infection but stage and activity require clinical context and titer.
• SerologySyphilis Treponemal Tests (TP-PA / FTA-ABS / EIA / CIA)Reactive: Treponemal antibody detected; may indicate current, past, or treated infection.
• Selective/Differential MediaTCBS AgarSucrose positive: Yellow colonies.
• Respiration/ReductionTellurite Reduction for MycobacteriaGray to black color or precipitate from tellurite reduction.
• Antimicrobial SusceptibilityTrimethoprim-Sulfamethoxazole (SXT) ScreenSusceptible: Zone or MIC meets the current susceptible criterion.
• Differential MediaTriple Sugar Iron Agar (TSI)A/A (acid/acid): Carbohydrate ferm. K/A: glucose, lactose, or sucrose fermentation. H2S production.
• Histology/MolecularTropheryma whipplei PAS and PCRSupportive histology: PAS-positive macrophages in compatible tissue.
• Enzyme/Spot TestsTween 80 HydrolysisIndicator shifts to pink or red from Tween 80 hydrolysis.
• Enzyme/CarbohydrateUrease Test (Christensen's)Slant changes from light orange to magenta (rapid producers may turn entire medium).
• Antimicrobial SusceptibilityVancomycin Screen for Catalase-Negative Gram-Positive RodsResistant screen: Growth up to the disk or no meaningful inhibition, supporting intrinsically resistant Gram-positive rod groups.
• Growth RequirementsVibrio Sodium Chloride RequirementHalophilic pattern: No growth without added NaCl and growth with added NaCl.
• Pigment/Colony TestsViolacein PigmentViolet to dark purple colony pigment.
• Microscopy/StainsWarthin-Starry Silver StainSmall dark-staining bacilli or clusters in a compatible tissue distribution.
• Historical SerologyWeil-Felix AgglutinationReactive: Agglutination with one or more Proteus antigens; not definitive for rickettsial disease.
• Growth RequirementsX and V Factor TestGrowth only around XV: Requires both X and V.