Used primarily in microbiology for the selective isolation and differentiation of Salmonella and Shigella species from clinical and food samples. The medium inhibits Gram-positive bacteria and many non-pathogenic Enterobacteriaceae through the action of bile salts and desoxycholate. Xylose and lysine serve as biochemical indicators: pathogenic Salmonella typically ferment xylose and decarboxylate lysine, producing alkaline byproducts that turn the medium red, while Shigella does not ferment xylose and fails to decarboxylate lysine, leaving the medium yellow or unchanging. The presence of thiosulfate allows detection of hydrogen sulfide production, indicated by black centers in colonies, which helps distinguish Salmonella from other organisms. Commonly used in food safety testing, outbreak investigations, and clinical diagnostics.