Used in microbiology to differentiate enteric bacteria based on their ability to ferment lactose and/or glucose and to detect hydrogen sulfide production. It helps identify members of the Enterobacteriaceae family by showing color changes in the medium: yellow indicates acid production from fermentation, red indicates no fermentation, and a black precipitate shows H₂S gas production. The slant and butt setup allows observation of differential metabolism under semi-aerobic (slant) and anaerobic (butt) conditions. Commonly used in clinical labs for stool sample analysis and pathogen screening.