m Endo Broth MF™ is used for enumerating coliform organisms in water by membrane filtration.

Principles m Endo Broth MF contains peptones as sources of carbon, nitrogen, vitamins and minerals. Yeast extract supplies B-complex vitamins, which stimulate bacterial growth. Lactose is the carbohydrate. Phosphates are buffering agents. Sodium chloride maintains the osmotic balance of the medium. Sodium desoxycholate and sodium lauryl sulfate are added as inhibitors of gram-positive bacteria. Basic fuchsin is a pH indicator. Sodium sulfite is added to decolorize the basic fuchsin solution. The ethanol additive increases the antibacterial nature of the formulation.

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.