Used in microbiology laboratories to isolate and differentiate gram-negative bacteria, particularly members of the Enterobacteriaceae family, based on their ability to ferment lactose. It is commonly used in clinical diagnostics, food and water testing, and pharmaceutical quality control. The medium inhibits gram-positive bacteria using bile salts and crystal violet, allowing selective growth of gram-negative organisms. Lactose fermenters form pink colonies due to acid production, while non-fermenters appear colorless or pale. This helps in the preliminary identification of pathogens such as Escherichia coli, Salmonella, and Shigella.