For customer preparation of microbiological media. m-Endo broth is used for detection of total coliform bacteria using the membrane filtration method. m-Endo broth detects total coliform bacteria (colonies with a greenish-gold sheen). Lactose-fermenting bacteria produce acetaldehyde that reacts with the sodium sulfite and fuchsin to form red colonies. The development of a metallic sheen occurs when the organism produces aldehydes with the rapid fermentation of lactose. If the inoculum is too heavy, the sheen will be suppressed. Lactose-nonfermenting bacteria form clear, colorless colonies. For potable water samples, confirm with Lauryl Tryptose and Brilliant Green Bile Broth tubes. Samples that test positive for total coliform bacteria should be further analyzed for the presence of fecal coliform or E. coli using EC Medium or EC Medium with MUG respectively.