With routine testing of milk and milk products vital to consumer safety and product quality, detecting potential pathogens as quickly and easily as possible is of paramount importance. The ability to enumerate presumptive Escherichia coli from presumptive coliforms, for instance, rapidly flags up any contamination problems.
Lab M’s modified lauryl sulphate tryptose broth with MUG and tryptophan (ISO) is designed specifically for this purpose, enabling the presumptive enumeration of E. coli from milk and milk products using the most probable number (MPN) technique according to ISO 11866-1:2005. The ISO specifications indicate that this technique can be applied not only to milk but also to a wide range of liquid and dried milk products, cheese, butter, ice creams, custard, desserts and cream.
The key to E. coli enumeration is the addition of 4-methylumbelliferyl-?-D-glucuronide (MUG) to the standard lauryl tryptose broth formulation, allowing positive discrimination of strains. The majority produce ?-glucuronidase enzyme, resulting in hydrolysis of MUG and the release of a fluorogenic compound. Tubes which fluoresce under UV light are confirmed for E. coli by a positive indole reaction when Kovac’s reagent is added to the tube.