prEN ISO 9308-4

Water quality - Enumeration of Escherichia coli and coliform bacteria - Part 4: Membrane filtration method for Escherichia coli in water with high levels of background bacteria (ISO/DIS 9308-4:2025)

Publication date:   Nov 20, 2025

Scope

This document describes a highly specific method for the enumeration of Escherichia coli (E. coli) in water. The method is based on membrane filtration, subsequent culture at 44 °C on a chromogenic agar medium containing a chromogenic ingredient for the detection of the enzyme ß-glucuronidase, and calculation of the number of target organisms in the sample.
Because of the high specificity of the method, this document is suitable for waters with high levels of background bacteria, such as surface waters including bathing water and wastewater. E. coli strains which do not grow at 44 °C and those that are β-glucuronidase negative, such as E. coli O157, will not be detected as E. coli by this method.