Microbial Culture Media and Biochemical Tests for Bacterial Identification

Thayer-Martin Agar

Selective for Neisseria. N. gonorrhoeae (glucose only), N. meningitidis (glucose + maltose).

Chocolate Agar

Enriched medium providing X & V factors; supports Neisseria and Haemophilus.

Blood Agar

Non-selective differential medium; N. meningitidis grows, N. gonorrhoeae does not.

Bordet-Gengou / Regan-Lowe Agar

Selective for Bordetella pertussis; produces pearly colonies, requires 10% CO₂.

Catalase Test

Distinguishes Staphylococcus/Listeria (positive) from Streptococcus/Enterococcus (negative).

Motility

Positive for B. cereus and Listeria (at 25°C); negative for B. anthracis.

Hemolysis on Blood Agar

β-hemolysis (Listeria, B. cereus); γ-hemolysis (B. anthracis).

CAMP Test

Synergistic hemolysis; positive for Listeria and Group B Streptococcus (GBS).

Tinsdale Agar

Selective/differential for Corynebacterium diphtheriae; black colonies with brown halo.

TCBS Agar

Selective and differential for Vibrio species. Yellow = V. cholerae (sucrose +); Green = V. parahaemolyticus or V. vulnificus (sucrose -).

MacConkey Agar

Differentiates lactose fermenters. Pink/red colonies = Klebsiella, colorless = Pseudomonas.

TSI Slant

Tests glucose/lactose/sucrose fermentation and H₂S production. V. cholerae A/A no gas; Klebsiella A/A + gas no H₂S.

Oxidase Test

Distinguishes non-Enterobacteriaceae (positive). Vibrio and Pseudomonas are oxidase +.

Urease / Indole Tests

Used for Klebsiella speciation. K. oxytoca = Indole +; K. pneumoniae = Indole -.

TSI K/A Reaction

Glucose only (red/yellow); examples: Shigella, Salmonella.

TSI A/A Reaction

Lactose/sucrose + glucose fermentation; examples: E. coli, Proteus vulgaris.

TSI Black Butt

Indicates H₂S production; examples: Salmonella, Proteus.

TSI Gas Bubbles/Lifting

Indicates CO₂ or H₂ gas from fermentation; typical of strong fermenters.

Motility (Differentiation Highlight)

Positive: E. coli, Salmonella, Proteus; Negative: Shigella, Klebsiella.

Lactose Fermentation (Differentiation Highlight)

Positive: E. coli, Klebsiella; Negative: Salmonella, Shigella, Proteus.

H₂S Production (Differentiation Highlight)

Positive: Salmonella, Proteus; Negative: E. coli, Shigella.

Urease (Differentiation Highlight)

Positive: Proteus, Klebsiella; Negative: E. coli, Salmonella, Shigella.

Indole (Differentiation Highlight)

Positive: E. coli, Proteus vulgaris; Negative: Klebsiella, Salmonella.