ISO 9308-1:20 14规定了大肠杆菌（E.coli）和大肠菌群的计数方法。该方法基于膜过滤，随后在显色大肠菌群琼脂培养基上培养，并计算样品中目标生物的数量。由于差异琼脂培养基的低选择性，背景生长可能干扰例如地表水或浅井水中大肠杆菌和大肠菌群的可靠计数。这种方法不适用于这些类型的水。 ISO 9308-1:20 14特别适用于细菌数量较低的水域，这些水域会导致显色大肠菌群琼脂（CCA）上的菌落总数少于100个。这些可能是饮用水、消毒池水或饮用水处理厂的成品水。一些β-D-葡糖醛酸糖苷酶阴性的大肠杆菌菌株，如大肠杆菌O157，将不会被检测为大肠杆菌。由于它们是β-D-半乳糖苷酶阳性，它们将在该显色琼脂上表现为大肠菌群。

ISO 9308-1:2014 specifies a method for the enumeration of Escherichia coli (E. coli) and coliform bacteria. The method is based on membrane filtration, subsequent culture on a chromogenic coliform agar medium, and calculation of the number of target organisms in the sample. Due to the low selectivity of the differential agar medium, background growth can interfere with the reliable enumeration of E. coli and coliform bacteria, for example, in surface waters or shallow well waters. This method is not suitable for these types of water. ISO 9308-1:2014 is especially suitable for waters with low bacterial numbers that will cause less than 100 total colonies on chromogenic coliform agar (CCA). These may be drinking water, disinfected pool water, or finished water from drinking water treatment plants. Some strains of E. coli which are β-D-glucuronidase negative, such as Escherichia coli O157, will not be detected as E. coli. As they are β-D-galactosidase positive, they will appear as coliform bacteria on this chromogenic agar.