Used for the presumptive identification of coliforms and the determination of the presence of Escherichia coli in water samples by a presence/absence technique. Bromocresol purple is a pH indicator that demonstrates a color change from purple to yellow in the presence of acid. Lactose fermenting organisms produce acid, which initiates the color change. The presence of coliforms is detected with greater sensitivity by use of a relatively large sample volume (100mL) in a single bottle. The additional of MUG (4-methylumberlliferyl-b-D-glucuronide), which is a fluorogenic substrate, allows the media to selectively identify Escherichia coli. MUG is hydrolyzed by the Escherichia coli specific enzyme b-glucuronidase to release 4-methylumbelliferone, which fluoresces under ultraviolent light (approx. 366mm wavelength).