ISO 16649-2:2001

The enumeration of presumptive Escherichia coli requires the successive stage after the preparation of initial suspension using as diluent peptone water (or the specific International Standard dealing with the product under examination).

Isolation: inoculation of chromogenic selective culture medium (TBX) with the specified quantity of the initial suspension and dilutions.

Inoculation, under the same conditions, using decimal dilutions of the test sample or of the initial suspension, with 2 plates per dilution.

Incubation of the dishes 18-24h at 44°C and examination to check for the presence of CFU which, from their characteristics, are considered to be Escherichia coli.

Enumeration: calculation of the number of colony-forming units (CFU) of presumptive Escherichia coli per gram or per millilitre of sample.