SS agar medium (Salmonella Shigella agar) is a highly selective medium commonly used for intestinal bacteria. It is mainly used for the screening of Salmonella and Shigella. These two bacteria form on SS medium. Colorless colonies that do not decompose lactose, and non-pathogenic intestinal bacteria such as Escherichia coli are mostly pink colonies that decompose lactose.

SS is the initials of Salmonella and Shigella.