The Identification "Matrix" (Biochemical Tests)

CNA Agar Selectivity

Selects for Gram-positive organisms; inhibits Gram-negatives using colistin and nalidixic acid.

Catalase Test Target

Tests for an enzyme that converts H2O2 into water and oxygen.

Catalase Test Positive Result

Produces visible, rapid bubbles.

Coagulase Test Target

Identifies S. aureus by testing for enzyme activity.

Coagulase Test Positive Result

Produces a large clot or fibrin threads in plasma.

Bile Esculin Test Purpose

Differentiates Enterococcus from Streptococcus.

Bile Esculin Test Positive Result

Turns dark brown or black.

Oxidase Test Target

Tests for cytochrome c oxidase.

Oxidase Test Positive Result

Indicator dye turns from colorless to blue (e.g., Pseudomonas).

Indole Test Target

Detects the breakdown of tryptophan by bacteria.

Indole Test Positive Result

Produces a red ring at the top of the culture (e.g., E. coli).

Methyl Red (MR) Test Target

Tests for mixed-acid fermentation.

Methyl Red (MR) Test Positive Result

Turns red when pH drops below 4.4.

Voges-Proskauer (VP) Test Target

Detects acetoin from the 2,3-butanediol pathway.

Voges-Proskauer (VP) Test Positive Result

Produces a pink color.