This HiDip slides are recommended for direct Escherichia coli identification under UV light (366nm). CLED Agar- A non-selective agar based on lactose fermentation with Bromothymol blue, BTB as indicator. MUG MacConkey Agar - A selective medium for detection of Enterobacteriaceae and is based on lactose fermentation with neutral red as indicator. Bile salts mixture and crystal violet is the selective agent.. MUG is utilized by E.coli which contains beta glucuronidase and shows fluorescence under UV light. .