ISO 9308-2:20 12规定了水中大肠杆菌和大肠菌群的计数方法。该方法基于目标生物在液体培养基中的生长和通过参考MPN表计算生物的“最可能数”(MPN)。该方法可应用于所有类型的水，包括那些含有可观量的悬浮物和高背景计数的异养细菌。然而，它不得用于海水中大肠菌群的计数。当用于海水中大肠杆菌的计数时，通常需要在无菌水中稀释1→10，尽管该方法已被证明对一些盐浓度低于正常浓度的海水有效。在没有数据支持使用不稀释的方法的情况下，使用1→10稀释。该方法依赖于基于酶b的表达来检测大肠杆菌？D？葡萄糖醛酸酶，因此不能检测到通常不表达这种酶的大肠杆菌的许多肠出血菌株。此外，还有少量其他大肠杆菌菌株不表达b？D？葡萄糖醛酸酶。 用于检测和确认包括大肠杆菌在内的大肠菌群的细菌的测试的选择可以被视为连续序列的一部分。特定样本的确认程度部分取决于水的性质，部分取决于检查的原因。ISO 9308-2:20 12中描述的检测提供了确认的结果，无需进一步确认阳性孔。

ISO 9308-2:2012 specifies a method for the enumeration of E. coli and coliform bacteria in water. The method is based on the growth of target organisms in a liquid medium and calculation of the "Most Probable Number" (MPN) of organisms by reference to MPN tables. This method can be applied to all types of water, including those containing an appreciable amount of suspended matter and high background counts of heterotrophic bacteria. However it must not be used for the enumeration of coliform bacteria in marine water. When using for the enumeration of E. coli in marine waters, a 1→10 dilution in sterile water is typically required, although the method has been shown to work well with some marine waters that have a lower than normal concentration of salts. In the absence of data to support the use of the method without dilution, a 1→10 dilution is used. This method relies upon the detection of E. coli based upon expression of the enzyme b？D？glucuronidase and consequently does not detect many of the enterohaemorhagic strains of E. coli, which do not typically express this enzyme. Additionally, there are a small number of other E. coli strains that do not express b？D？glucuronidase. The choice of tests used in the detection and confirmation of the coliform group of bacteria, including E. coli, can be regarded as part of a continuous sequence. The extent of confirmation with a particular sample depends partly on the nature of the water and partly on the reasons for the examination. The test described in ISO 9308-2:2012 provides a confirmed result with no requirement for further confirmation of positive wells.