Tetrathionate Broth Base, with iodine-iodide solution, is used as a selective enrichment for the cultivation of Salmonella species that may be present in low numbers or have been injured during food processing, and compete with other microorganisms and intestinal flora. Even though cells which have been injured might not form colonies on selective media, they can cause disease if ingested. This formulation conforms to the United States Pharmacopoeia (USP). Tetrathionate is formed by the iodine reaction with Sodium thiosulfate. This combination (Sodium thiosulfate and Tetrathionate) suppresses commensal intestinal organisms. The organisms which have the enzyme tetrathionate reductase, such as Salmonella, proliferate in this medium. However, Proteus also contains this enzyme, but its growth can be minimized by adding 4 mg /l of novobiocin before adding the iodine solution. Peptone provides nitrogen, vitamins, minerals and amino acids essential for growth. Bile salts are inhibitors of other Gram-positive organisms. Calcium carbonate neutralizes and absorbs toxic metabolites.
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