TBX Chromogenic Agar (Tryptone Bile X-Glucuronide) is based on Tryptone Bile Salts Agar medium, used to detect and enumerate E. coli in foods, with the addition of a chromogenic agent, x-ÃŸ-D-Glucuronide, to detect the presence of the enzyme glucuronidase, which is highly specific for E. coli. The released chromophore in TBX Agar is colored and target colonies are easily identified. E. coli absorbs the chromogenic agent x-ÃŸ-D-glucuronide, and the intracellular glucuronidase enzyme activity breaks the bond between the chromophore and the glucuronide. The released chromophore is colored and builds up within the cells, causing the E. coli colonies to be blue-green colored. Casein peptone provides nitrogen, vitamins, minerals and amino acids essential for growth. Bile Salts are inhibitors to other Gram-positive organisms and suppress coliform bacteria. Bacteriological agar is the solidifying agent. ISO 16649 specifies a horizontal method for the enumeration of ÃŸ-glucuronidase-positive E. coli in products intended for human consumption or for the feeding of animals. The negative b-ÃŸ-glucuronidase E. coli colonies are colorless, e.g. E. coli O157: H7. The high temperatures (44°C) inhibit the growth of E. coli O157: H7.
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