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RS ISO 9308-2: 2012
Water quality ? Detection and enumeration of Escherichia coli and coliform bacteria — Part 2: Most probable number method

Abstract

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 ?-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
?-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.

General Information

Code	Classification	Theme	Pages	Publisher	Availability
RS ISO 9308-2: 2012	ADOPTED ISO STANDARDS	Environment. Health protection. Safety	55	Second Edition Oct 2022	Available