Stool from a patient with suspected cholera is cultured on thiosulfate citrate bile salts sucrose (TCBS) agar. Colonies of Vibrio cholerae appear yellow on this medium because the organism:
- A Hydrolyzes bile salts releasing pigment
- B Reduces thiosulfate to hydrogen sulfide
- C Ferments sucrose producing acid ✓
- D Produces oxidase that changes the indicator color
Correct answer: C. Ferments sucrose producing acid
Explanation
TCBS contains bromothymol blue and thymol blue indicators along with high pH, bile salts, thiosulfate, citrate, and sucrose. Vibrio cholerae ferments sucrose, generating acid that turns the indicators so colonies appear yellow, whereas organisms unable to ferment sucrose produce green colonies. Thiosulfate reduction relates to hydrogen sulfide production seen in Salmonella, not vibrios, and oxidase positivity is tested separately and does not color colonies.
Reference: Ananthanarayan and Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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