Violet Red Bile Agar is used to determine which count?

• A. Bacteria Count
• B. Coliform Count
• C. Somatic Cell Count
• D. Yeast Count

Answer: (B)

Violet Red Bile Agar is a selective-differential medium designed to isolate and count coliform bacteria. It includes bile salts and crystal violet to suppress many non-enteric and Gram‑positive organisms, while lactose and a neutral red indicator allow lactose-fermenting bacteria to be distinguished. Coliforms ferment lactose, producing acid that turns their colonies red on the purple agar, making them easy to count. Non-coliforms either don’t ferment lactose or are inhibited, so they don’t show up as the characteristic red colonies. That’s why this medium is used to determine the coliform count, a key measure of sanitary quality in foods and water.