Salmonella Shigella (SS) Agar is a selective and differential medium used for the isolation and cultivation of Salmonella species from clinical and non-clinical specimens.
It was developed to aid in the differentiation of lactose and non-lactose-fermenters from suspected food samples.
SS Agar is a moderately selective medium that inhibits gram-positive bacteria using bile salts, brilliant green, and sodium citrate.
Salmonella Shigella (SS) Agar is highly selective for Salmonella but inhibitory to some strains of Shigella. The inclusion of Bile Salts, Sodium Citrate, and Brilliant Green serve to inhibit gram-positive coliform organisms and inhibit swarming Proteus spp. while allowing Salmonella spp. to grow.
Differentiation of enteric organisms is achieved by the incorporation of lactose in the medium.
Organisms that ferment lactose produce acid, which results in the formation of red/pink colonies. Lactose-non-fermenters form colorless colonies.
The medium also contains indicators to detect hydrogen sulfide by the production of colonies with black centers. The medium is not recommended for primary isolation of Salmonella but is used for differentiation of lactose fermenting and non-fermenting enteric bacteria.
Some non-pathogenic organisms may grow on the medium, which is why it is recommended that biochemical, immunological, molecular, or mass spectrometry testing be performed on colonies from pure culture for complete identification. It is important to note that the incubation period and result interpretation may vary based on the sample source and testing protocol.