Indicator used in MaConkey Agar ?

Ans. is 'c' i.e., Neutral red MacConkey agar is a selective medium for enteric gram negative bacilli. It is used to differentiate lactose fermenting enteric bacilli from lactose non-fermenters. Composition of MacConkey agar ? 1) Enzymatic digest of gelatin, casein and animal tissue : To provide nutrition. 2) Lactose : Fermentable carbohydrate. 3) Bile salts : Selective agent and inhibits gram positive organisms. 4) Crystal violet : Inhibits gram positive bacteria. 5) Sodium chloride : Supplies essential electrolytes and osmotic balance. 6) Neutral red : pH indicator (when lactose is fermented, the pH of medium decreases, changing color of neutral red to pink). 7) Agar : Solidifying agent.