MCQ of the Day: 2 November 2026

Answer: A. Thiosulphate-citrate-bile salts-sucrose (TCBS) agar

Rice-water stools without fever, comma-shaped bacilli with darting motility immobilised by antiserum, and enrichment in alkaline peptone water point to cholera (Vibrio cholerae O1), which remains endemic in India. TCBS is the selective medium of choice: its high pH, bile salts and citrate suppress most enteric flora, and V. cholerae ferments sucrose, giving yellow colonies. V. parahaemolyticus does not ferment sucrose and grows as green colonies. Venkatraman-Ramakrishnan (VR) medium and Cary-Blair are used for transport.

B (MacConkey): V. cholerae is a late lactose fermenter, so colonies are colourless at first and only later turn pink; the medium is not selective enough to stand out in stool.

C (XLD): designed for Salmonella and Shigella (red colonies, black centres for H2S producers), not vibrios.

D (DCA): selective for Salmonella and Shigella; vibrios grow poorly and give no characteristic yellow colonies.