ISO 21528-2:2004 specifies a method, without pre-enrichment, for the enumeration of Enterobacteriaceae. It is applicable to products intended for human consumption and the feeding of animals, and environmental samples in the area of food production and food handling.
Enumeration is carried out by counting colonies in a solid medium after incubation at 37 °C.
This technique is recommended when the number of colonies sought is expected to be more than 100 per millilitre or per gram of the test sample.