Overview

The presence and extent of faecal pollution is an important factor in assessing the quality of a body 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 a failure in treatment or ingress of water into the distribution system. ISO 9308 consists of the following parts, under the general title Water quality - Enumeration of Escherichia coli and coliform bacteria: - Part 1: Membrane filtration method for waters with low bacterial background flora; - Part 2: Most probable number method; - Part 3: Miniaturized method (Most Probable Number) for the detection and enumeration of E. coli in surface and waste water. This part of ISO 9308 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 beta-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 beta-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 this part of ISO 9308 provides a confirmed result with no requirement for further confirmation of positive wells. The text of ISO 9308-2:2012 has been prepared by Technical Committee ISO/TC 147 "Water quality" and has been taken over as EN ISO 9308-2:2014 by Technical Committee CEN/TC 230 "Water analysis" (secretariat: DIN, Germany). The responsible German body is subcommittee NA 119-01-03-03 UA "Mikrobiologie" ("Microbiology") of Working Committee NA 119-01-03 AA "Wasseruntersuchung" ("Water examination") of DIN Standards Committee Water Practice (NAW).

Document: references other documents

Responsible national committee

NA 119-01-03-03 UA - Microbiology  

Responsible european committee

CEN/TC 230 - Water analysis  

Responsible international committee

ISO/TC 147/SC 4 - Microbiological methods