Which agar is recommended for the selective isolation of Vibrio spp.?

• A. Charcoal yeast extract agar
• B. Mannitol salt agar
• C. Tinsdale agar
• D. Thiosulfate-citrate-bile salt-sucrose agar

Answer: (D)

Selective isolation of Vibrio spp. relies on using a medium that inhibits many competing organisms while supporting Vibrio growth and revealing its sugar fermentation. Thiosulfate-citrate-bile-salt-sucrose agar (TCBS) does exactly that: bile salts and a high pH suppress many other bacteria, while the alkaline, salt-rich environment favors Vibrio. The sucrose and a pH indicator make the result differential, as Vibrio species that ferment sucrose form yellow (acidic) colonies, whereas nonfermenters stay green. This combination of selective suppression and differential indication makes TCBS the preferred medium for isolating Vibrio. In contrast, charcoal yeast extract agar is designed for Legionella and isn’t selective for Vibrio; mannitol salt agar selects Staphylococcus due to high salt content and would not favor Vibrio; and Tinsdale agar targets Corynebacterium diphtheriae with tellurite, not Vibrio.