This part of ISO 11866|IDF 170 specifies a combined method for the enumeration of presumptive Escherichia coli and of presumptive coliforms by means of a culture technique involving a liquid medium with MUG, and calculation of the number of presumptive Escherichia coli and/or coliforms per gram or per millilitre by the most probable number (MPN) technique after incubation at 30 °C. It is a more rapid method than that described in ISO 7251 as the incubation time is reduced omission of several enrichment steps. The method is applicable to — milk, liquid milk products, — dried milk, dried sweet whey, dried buttermilk, lactose, — acid casein, lactic casein and rennet casein, — caseinate and dried acid whey, — cheese and processed cheese, — butter, — frozen milk products (including edible ices), and — custard, desserts and cream. The method specified in this part of ISO 11866|IDF 170 is preferred for samples in which comparatively low numbers of presumptive Escherichia coli and/or other presumptive coliforms (less than 100 per gram or 10 per millilitre) are suspected. CAUTION — The applicability of this part of ISO 11866|IDF 170 is limited by the susceptibility of the method to a large degree of variability. The method should, therefore, be applied and the results interpreted in the light of the information given in Clause 12. NOTE The methods described in ISO 4831 apply for the enumeration of coliforms for reference purposes.