Tryptone, polyvalent peptone and yeast powder supply nitrogen sources, vitamins and growth factors for bacterial growth. Sodium chloride maintains osmotic balance. Lactose acts as fermentable carbohydrate. No.3 bile salt suppresses Gram-positive bacteria. Agar serves as the gelling agent. Aniline blue and rose acid function as combined pH indicators.
Fecal coliforms ferment lactose and generate acid at 44.5 ℃, lowering the pH of the medium and forming bright blue colonies. Other non-lactose-fermenting enteric bacteria develop colorless, gray or light red colonies.
