ISO/TS 16649-3:2005

Inoculation of three tubes* of liquid selective enrichment medium (minerals modified glutamate medium) with a specified quantity of the test sample if the initial product is liquid, or with a specified quantity of the initial suspension in the case of other products. Then, under the same conditions, inoculation of the medium with decimal dilutions of the test sample or the initial suspension.

Incubation of the tubes of medium at 37°C for 24. Examination of the tubes for acid production, signifying lactose fermentation.

For each tube of medium showing acid production, subculture to tryptone bile glucuronide agar.

Incubation of the tryptone bile glucoronide agar at 44°C for 20-24h. Examination of the tryptone bile glucoronide agar for the presence of blue colonies, signifying the presence of β-D-glucoronidase positive Escherichia coli.

Determination of the most probable number of presumptive Escherichia coli by means of the MPN table, according to the number of tubes of medium the subcultures of which have produced blue colonies on tryptone bile glucoronide agar.

*or five tubes