Which medium is selective for Vibrio species due to its composition of bile salts and sucrose?

• A. MacConkey
• B. Thiosulfate-citrate-bile salts-sucrose agar
• C. Blood agar
• D. Chocolate agar

Answer: (B)

Thiosulfate-citrate-bile salts-sucrose agar isolates Vibrio by combining two key features: bile salts to suppress many other bacteria and sucrose with a pH indicator to differentiate organisms that can ferment that sugar. The bile salts inhibit most non-Vibrio organisms, so Vibrio species, which tolerate them, are able to grow. The medium uses sucrose as the fermentable carbohydrate; when a Vibrio ferments sucrose, acid is produced and the colony turns yellow against the background, making it easy to distinguish. Non-sucrose-fermenting bacteria either don’t grow well or don’t produce the color change, so they’re not mistaken for Vibrio. Other media like MacConkey, blood, or chocolate agar lack this targeted combination of bile salts plus a fermentable sugar with differential color change, so they’re not selective for Vibrio in the same way.