DIN EN ISO 9308-1:2014-12

This standard 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. This standard is especially suitable for waters with low bacterial numbers that will cause less than 100 total colonies on chromogenic coliform agar. 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. The presence and extent of faecal pollution is an important factor in assessing the quality of water and the risk to human health from infection. Examination of water samples for the presence of Escherichia coli (E. coli), which normally inhabits the bowel of man and other warm-blooded animals, provides an indication of such pollution. Examination for coliform bacteria can be more difficult to interpret because some coliform bacteria live in soil and surface fresh water and are not always intestinal. Therefore, the presence of coliform bacteria, although not a proof of faecal contamination, may indicate failure in treatment, storage, or distribution. This document has been prepared by Technical Committee ISO/TC 147 "Water quality" in collaboration with Technical Committee CEN/TC 230 "Water analysis" (secretariat: DIN, Germany). The responsible German body is Standards Committee Water Practice, Subcommittee NA 119-01-03-03 UA "Mikrobiologie" ("Microbiology") of Working Committee NA 119-01-03 AA "Wasseruntersuchung" ("Water examination").