For presumptive identification of coliforms from water. MacConkey Broth Purple w/ BCP is a modification of MacConkey Medium. MacConkey Broth Purple w/ BCP is recommended by ISO committee with the inclusion of bile salts, as a presumptive test medium for identification of coliforms from water and other materials of sanitary importance. Lactose fermenting organisms turn the medium yellow due to the acidity produced on lactose fermentation. The colour change of the dye is observed when the pH of the medium falls below 6.8. Lactose non-fermenting organisms like Salmonella and Shigella do not alter the appearance of the medium. Medium contains Peptic digest of animal tissue which provides essential growth nutrients. Lactose is the fermentable carbohydrate. Bile salts or sodium taurocholate inhibits gram-positive organisms. Sodium chloride maintains the osmotic balance of the medium. In this medium, neutral red is substituted by the less inhibitory bromocresol purple dye Bromocresol purple is the pH indicator in the medium, which turns yellow under acidic condition.