S-S agar refers to Shigella-Salmonella agar. The nutrient medium is a foreign counterpart "Ploskirev baktoagar". The difference lies in the strong, sometimes complete, inhibition of concomitant microflora. In addition to SS-agar is not used iodine. The selective agents, in this case, are the bile, brilliant green, thiosulfate. The nutrient medium also reveals the fermentation of lactose by redness of the colonies and the development of hydrogen sulfide on blackening.