They used EMB agar to clearly differentiate between the colonies of lactose fermenting and nonfermenting microbes. In the same medium, sucrose was also included to differentiate between coliforms that were able to ferment sucrose more rapidly than lactose and those that were unable to ferment sucrose. Lactose fermenter colonies were either black or possessed dark centers with transparent and colorless outer margins, while lactose or sucrose nonfermenters were colorless.