Description

EMB contains lactose and sucrose sugars, but it is the lactose that is the key to the medium. Lactose-fermenting bacteria (E. coli and other coliforms) produce acid from lactose use, and the combination of the dyes (which serve as pH indicators in this medium) produces color variations in the colonies because of the acidity. Strong acidity produces a deep purple colony with a green metallic sheen, whereas less acidity may produce a brown-pink coloration of colony. Nonlactose fermenters appear as translucent or pink.