Eosin Methylene Blue Agar is a weakly selective medium used to isolate gram-negative intestinal bacteria, especially Escherichia coli and fecal coliforms. The medium provides carbon and nitrogen sources from protein peptone; lactose, a sugar that can be fermented by Escherichia coli; potassium dihydrogen phosphate as a buffer; and agar as a solidifying agent. Eosin and methylene blue are used as inhibitors of gram-positive bacteria and as indicators that produce precipitates under acidic conditions, forming purple-black colonies or colonies with a black center and a colorless transparent periphery.
