This part of ISO 9308 specifies a method for the payment of E. coli and coliform bacteria in water. The method is based on the propagation of target organisms in a liquid medium and the 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 a significant amount of suspended solids and a high count of heterotrophic accompanying bacteria. However, it must not be used to control coliform bacteria in seawater. When the method is used to pay for E. coli in seawater, a 1:10 dilution in sterile water is usually required, although the method has been shown to work well with some seawater that has a lower than usual salt concentration. If there is no data to support the use of the non-dilution method, a 1:10 dilution is used. This method relies on the detection of E. coli based on the expression of the enzyme D-glucuronidase and consequently many of the enterohamorrhagic strains of E. coli, which do not usually express this enzyme, are not detected. There are also a small number of other E. coli strains that do not express -D-glucuronidase. The selection of assays used to detect and confirm the coliform group of bacteria, including E. coli, can be viewed as part of a continuous sequence. The extent of confirmation for a particular sample depends partly on the nature of the water and partly on the reasons for the examination. The examination described in this part of ISO 9308 provides a confirmed result without the need for further confirmation of positive wells. NOTE During the procedure the use of a commercially available payment device
EN ISO 9308-2:2014 Referenced Document
ISO 19458:2006 Water quality - Sampling for microbiological analysis
ISO 8199:2005 Water quality - General guidance on the enumeration of micro-organisms by culture
ISO/IEC Guide 2:2004 Standardization and related activities - General vocabulary
ISO/TR 13843:2000 Water quality - Guidance on validation of microbiological methods
EN ISO 9308-2:2014 history
2014EN ISO 9308-2:2014 Water quality - Enumeration of Escherichia coli and coliform bacteria - Part 2: Most probable number method