For laboratory diagnosis of cholera, stool from a suspected case is plated on thiosulfate citrate bile salts sucrose (TCBS) agar. Colonies of Vibrio cholerae appear as:

• A Green colonies due to sucrose non-fermentation
• B Large yellow colonies due to sucrose fermentation ✓
• C Black colonies with a metallic sheen due to H2S production
• D Pink flat lactose-fermenting colonies

Explanation

TCBS is the selective medium of choice for vibrios. Vibrio cholerae ferments sucrose, producing large smooth yellow colonies after overnight incubation, while sucrose-negative vibrios such as V. parahaemolyticus form green colonies. This color difference allows presumptive identification at the bench before confirmatory slide agglutination with O1 antiserum. H2S-producing black colonies characterize Salmonella on media such as XLD or Wilson and Blair, not TCBS, which contains no indicator for H2S.

Reference: Ananthanarayan and Paniker's Textbook of Microbiology, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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