It differentiates the gram-negative bacteria based on their lactose metabolism. The lactose fermenting bacteria, such as Escherichia coli, Klebsiella spp, Citrobacter, and Enterobacter forms pink-red colonies, while lactose non-fermenters, like Salmonella, Shigella, Proteus, Providencia, Pseudomonas, and Morganella form pale or colorless colonies