salmonella shigella agar for differential and selective isolation of Salmonella and Shigella species from pathological samples.
SALMONELLA SHIGELLA AGAR (SS AGAR) is used for differential and selective isolation of Salmonella and Shigella species from pathological samples and foods. Shigella is a genus of Gram-negative, non-spore forming rod-shaped bacteria closely related to Escherichia coli and Salmonella.. The causative agents of human shigellosis, Shigella cause disease in primates, but not in other mammals. Salmonella is a genus of rod-shaped, Gram-negative, non-spore forming, predominantly motile enterobacteria. They cause illnesses in humans and many animals, such as typhoid fever, paratyphoid fever, and the food borne illness salmonellosis. This medium consists of Beef extract and Peptic digest of animal tissue provide nitrogen, vitamins, minerals and amino acids essential for growth. Lactose is the fermentable carbohydrate providing carbon and energy. Bile salts and Sodium citrate inhibit Gram-positive bacteria, most coliform bacteria and swarming Proteus spp., while allowing Salmonella spp to grow. Brilliant green and high concentrations of Sodium thiosulphate and citrate largely inhibit the accompanying microbial flora. Sulphide production is detected by using thiosulphate and iron ions, the colonies turn black. The presence of coliform bacteria is established by detecting degradation of lactose to acid with the pH indicator neutral red. Neutral red is the pH indicator. Non-lactose fermenting bacteria (supposed pathogens) produce clear colonies, transparent or colorless, while coliforms are sufficiently inhibited, and form small colonies that vary from pink to red in color. The plates of the medium can be kept for at least a week in refrigeration. This formulation, highly selective, is not recommended for the primary isolation of Shigella. Some Shigella spp. may be inhibited.