Leucine Aminopeptidase (LAP) Test: Principle, Procedure, Results
LAP (leucine aminopeptidase) test: principle, procedure, and expected results, and how it works alongside PYR to identify catalase-negative Gram-positive cocci.
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Enzyme Tests
Various Biochemical Test that are based on enzymatic activity of the microorganisms.
Casein Hydrolysis Test: Principle, Procedure, and Uses
The casein hydrolysis test detects caseinase on skim milk agar, shown by a clear zone around growth. Learn the principle, how to read the result, positive and negative organisms, a...
Urea Breath Test (UBT): Principle, Procedure, and Results
The urea breath test (UBT) detects active Helicobacter pylori infection. Learn the principle, the 13C and 14C versions, patient preparation, how the result is read (delta over base...
Elek Test (Elek's Gel Precipitation Test): Principle, Procedure, and Results
The Elek test (Elek's gel precipitation test) is an immunodiffusion test that shows whether a Corynebacterium diphtheriae strain produces diphtheria toxin. Learn the principle, pro...
Modified Oxidase (Microdase) Test: The DMSO Trick That Separates Micrococcus From Staphylococcus
The standard oxidase reagent fails on Gram-positive cocci, so the microdase test dissolves it in DMSO to reach the cytochrome c inside. A blue disk means Micrococcus (which has cyt...
Butyrate Disk Test: Principle, Procedure, Results, Uses
The butyrate disk test detects butyrate esterase to presumptively identify Moraxella catarrhalis by a blue color. Learn the principle, procedure, how to read the result, and why it...
API 20E Test: Procedure, Reading the 21 Reactions, and the 7-Digit Profile Code
How to set up, incubate, and read the API 20E strip: which wells need oil, which need reagents, how to run the 21st test (oxidase), and how to build the 7-digit profile number for...
Nitrocefin Test: Principle, Procedure, Uses, Limitations
The nitrocefin test (Cefinase) detects beta-lactamase by a yellow-to-red color change, predicting penicillin resistance in hours. Learn the principle, procedure, how to read the re...
Hippurate Hydrolysis Test: Principle, Procedure, Results
Hippurate hydrolysis test principle, classical and rapid ninhydrin procedures, for identifying Streptococcus agalactiae and other organisms.
ONPG Test: How to Catch the Lactose Fermenters That the Lactose Test Misses
Some organisms have the enzyme to ferment lactose but lack the transporter to get lactose into the cell, so a standard lactose test calls them non-fermenters. ONPG is a lactose loo...
Nitrate Reduction Test: Why Red Means Positive, Unless It Means Negative
A red color after adding sulfanilic acid and alpha-naphthylamine is positive. But if there is no red, you are not done: add zinc, and now red means negative. The nitrate test is th...
DNase Test: Three Ways to Read It, and Why It Confirms Staph aureus When Coagulase Won't
A DNase-positive result can look like a fading green, a bright pink, or a clear halo, depending on which agar you use. All three answer one question: did the organism destroy the D...
Bile-Esculin test for Enterococcus species
Bile esculin test principle, procedure, and interpretation for identifying Group D streptococci and Enterococcus species using esculin hydrolysis.
PYR Test: The 2-Minute Way to Call Group A Strep at the Bench
A cherry-red color within a minute means the organism makes pyrrolidonyl arylamidase, which among the streptococci points straight to Group A Strep, or to Enterococcus. It is faste...
Catalase Test: The 3-Second Test That Separates Staph from Strep, and Five Ways It Lies
Bubbles in 3 seconds means Staphylococcus. But red blood cells bubble, nichrome loops bubble, and enterococci grown on blood agar bubble weakly. Learn what the catalase test actual...
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