Harlequin® Tryptone Bile Glucuronide Agar (TBX)

Harlequin® Tryptone Bile Glucuronide Agar (TBX) is used for the enumeration of E. coli in food and animal feed and is not intended for use in the diagnosis of disease or other conditions in humans. Tryptone Bile Glucuronide Agar is recommended by ISO 16649-1:2001, ISO 16649-2:2001 and ISO 16649-3:2015 for enumeration of β-glucuronidase positive Escherichia coli in products intended for human consumption or for the feeding of animals. The medium contains tryptone as a source of nitrogen and amino acids, bile salts act as a selective against Gram-positive organisms and agar is the gelling agent. 5-bromo-4-chloro-3-indolyl-β-D-glucuronide (X-glucuronide) is a chromogen for the detection of the β-D-glucuronidase enzyme which is present in most E. coli* but not other coliforms. The intracellular enzyme present in E. coli is able to break the bond between the substrate and the chromophore which dimerizes is the presence of oxygen to form an insoluble colored compound within the cell. The accumulation of the colored chromophore results in blue colonies on the agar.

*96-97% of E. coli are β-D-glucuronidase positive. A notable exception is E. coli O157:H7