Bismuth Sulfite Agar is a highly selective and differential medium. It is recommended for the isolation of Salmonella species, especially S. typhi, from food and clinical specimens.

Principles Bismuth Sulfite Agar is selective due to the presence of inhibitors, and is differential on the basis of hydrogen sulfide production Beef extract and peptones provide nitrogen, vitamins and minerals. Dextrose is an energy source. Bismuth sulfite and brilliant green are selective agents, inhibiting most commensal gram-positive and gram-negative organisms other than Salmonella species and some Shigella species. Ferrous sulfate is an indicator for hydrogen sulfide production, which occurs when the hydrogen sulfide produced by Salmonella reacts with the iron salt. This reaction causes a black or green metallic colony and brown or black precipitate.