MacConkey Broth (Double Strength) w/ Neutral Red is recommended for primary isolation of coliforms from large samples such as water or waste water. Bile salts inhibits the gram-positive bacteria. The media turns pink in case of lactose fermentors and yellow in case of lactose non- fermenters, due to neutral red indicator. Escherichia coli and Klebsiella aerogenes grows luxuriantlly on the media and shows positive reaction for acid and gas production.