Tryptone Bile X-Glucuronide (TBX) Medium (Dehydrated)

Detect and enumerate Escherichia coli in food and animal feed samples with Thermo Scientific™ Oxoid™ Typtone Bile X-Glucuronide (TBX) Medium (Dehydrated). The medium meets the formulation and performance criterion laid down in ISO 16649^{1, 2, 3} and ISO 11133:2014⁴.

TBX Medium builds on the speed, reliability and recovery from frozen samples and detection of poor lactose fermenters offered by the original Tryptone Bile Agar^4,5, with the addition of a chromogenic agent, X-glucuronide, which detects glucuronidase activity, an enzyme shown to be highly specific for Escherichia coli⁶.

Use TBX Medium for selective detection and enumeration of Escherichia coli in food and animal feed samples.

• Selective: presence of bile salts in the medium provide selectivity against Gram-positive bacteria, particularly bacilli and fecal streptococci.
• Easy-to-read: due to the addition of chromogenic 5-bromo-4-chloro-3-indolyl-beta-D-glucuronide (X-glucuronide), E. coli appear as blue/green colonies.
• ISO compliant: meets the formulation and performance criteria laid down in ISO 16649 and ISO 11133:2014.

Most Escherichia coli strains can be differentiated from other coliforms by the presence of the enzyme glucuronidase. However, approximately 3 to 4% of Escherichia coli are glucuronidase negative, notably Escherichia coli O157 strains⁷.

The chromogen in TBX Medium is 5-bromo-4-chloro-3-indolyl-beta-D-glucuronide (X-glucuronide) and is targeted by glucuronidase. Escherichia coli cells are able to absorb this complex intact and intracellular glucuronidase splits the bond between the chromophore and the glucuronide. The released chromophore is colored and builds up within the cells, causing Escherichia coli colonies to be colored blue/green.

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