Yersinia Select Agar Base (ISO 10273) is a selective and differential medium when used with supplements. The formula is based on the CIN Agar described by Schiemann, and is recommended by ISO 10273 for the isolation and detection of presumptive pathogenic Yersinia enterocolitica from a variety of clinical and food samples. Antibiotics are added as a supplement in order to inhibit the accompanying flora. The growth of Yersinia is promoted by pyruvate as well as by the nutrients content in the base. Yersinia degrades the mannitol of the medium to an acid form; the colonies are turning to red color due to the neutral red indicator. Mannitol fermentation in the presence of neutral red produces a characteristic bulls-eye colony, colorless with a red center. Mannitol is the fermentable carbohydrate, source of carbon and energy. Enzymatic digest of gelatin and the enzymatic digest of casein and animal tissues provide nitrogen, vitamins, minerals and amino acids essential for growth. Yeast extract is a source of vitamins, particularly of the B-group. Sodium pyruvate is added as a source of energy and as a protective substance in order to overcome oxygen toxicity biologically produced by the organisms. Sodium chloride supplies essential electrolytes for transport and osmotic balance. Magnesium sulphate is an ion required in a large variation of enzymatic reactions, including DNA replication. Neutral red is the pH indicator. Selective inhibition of Gram-negative and Gram-positive organisms is obtained through crystal violet, sodium desoxycholate and Irgasan (triclosan). Cefsulodin and novobiocin improve the inhibition of normal enteric organisms.
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