Escherichia coli on MacConkey agar. There are many variations of MacConkey agar depending on the need (here MacConkey Agar No.3, Oxoid®). MacConkey agar contains bile salts (cholate, taurocholate) as inhibitor of the Gram-poitive flora and neutral red as acid production from lactose indicator. In the picture you can see red lactose-positive colonies of E.coli with bile precipitation around them.

Cultivation 24 hours, 37°C in an aerobic atmosphere.