<prompt> Indicator used in MaConkey Agar ?Methylene blueMethyl redNeutral redBromothymol blue  <response>: 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. 