Question

TCBS agar is used for the isolation of :

• A. Aeromonas hydrophila
• B. Vibrio cholerae
• C. Escherichia coli
• D. Listeria monocytogenes

Hint:

TCBS is the standard selective agar for the genus Vibrio. Yellow colonies on TCBS indicate sucrose fermenters like V. cholerae, while green colonies indicate non-fermenters like V. parahaemolyticus.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Selective media are formulated to support the growth of specific target bacteria while inhibiting other background microorganisms present in a sample.
Detailed Explanation:
TCBS Agar stands for Thiosulfate-Citrate-Bile Salts-Sucrose Agar.
- This is a highly selective and differential agar medium designed specifically for the isolation of pathogenic vibrios, such as {Vibrio cholerae and Vibrio parahaemolyticus, from clinical and food samples (especially seafood).
- The high pH ($8.6$) and concentration of bile salts and sodium thiosulfate inhibit gram-positive bacteria and most enterics.
- Vibrio cholerae ferments sucrose, producing acid that turns the pH indicator (bromothymol blue) yellow, resulting in distinctive yellow colonies on the green agar.
- Non-sucrose fermenting species (like Vibrio parahaemolyticus) produce green colonies.
Other media are used for the isolation of the other options:
- Escherichia coli (3) is typically isolated on MacConkey or EMB agar.
- Listeria monocytogenes (4) is isolated on PALCAM or Oxford agar.

Step 2: Final Answer:
TCBS agar is used for the selective isolation of Vibrio cholerae.