Tryptone Bile X-Glucuronide (TBX) Medium

Detect and enumerate Escherichia coli in food samples with Thermo Scientific™ Typtone Bile X-Glucuronide (TBX) Medium. 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^1,2, with the addition of a chromogenic agent, X-glucuronide, which detects glucuronidase activity: an enzyme shown to be highly specific for Escherichia coli³. The released chromophore in TBX Medium is insoluble and accumulates within the cell, making colored target colonies easy to identify

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 strains⁴.

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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