TCBS (thiosulfate citrate bile salts sucrose) agar is selective for Vibrio species. V. cholerae O1/O139 produces which colony appearance on TCBS?

• A Blue-green colonies — V. cholerae does not ferment sucrose
• B Yellow colonies — V. cholerae ferments sucrose, producing acid ✓
• C Pink colonies similar to E. coli on MacConkey agar
• D No growth — V. cholerae is inhibited by bile salts on TCBS

Explanation

V. cholerae produces yellow colonies on TCBS agar because it ferments sucrose, generating acid which turns the pH indicator (bromothymol blue) yellow. In contrast, V. parahaemolyticus is sucrose non-fermenting and produces blue-green (non-sucrose-fermenting) colonies on TCBS. TCBS contains sodium thiosulfate, sodium citrate, oxgall (bile salts), and sucrose as differential substrate, inhibiting gram-positive bacteria and most Enterobacteriaceae. Confirmation of V. cholerae requires agglutination with O1 or O139 polyvalent antisera.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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