Violet Red Bile Agar with MUG is often abbreviated as VRBA w/ MUG. This medium is used for the fluorogenic detection ofEscherichiacoliin food, milk, water, and other sanitary materials. Like Violet Red Bile Agar, it is a selective medium which detects the growth of Lactose-fermenting coliforms. Coliform colonies lower the pH of the medium, thus causing their colonies to look red (neutral red dye). Crystal Violet and Bile Salts inhibit the growth of Gram-positive microorganisms, while the addition of 4-methylumbelliferyl-β-D-glucuronide (MUG) allows for the rapid detection ofE.coli. MUG is used as a substrate to detect glucuronidase activity, since its degradation by this enzyme produces the fluorescent compound 4-methylumbelliferone, visible under UV light.