This Standard sets out a method, using membrane filtration, for enumerating Escherichia coli (E. coli) and thermotolerant coliforms in water other than packaged water. Where waters are expected to contain low to moderate numbers of background bacteria, use of membrane lauryl sulfate agar or broth (m-LS) is recommended as the primary isolation medium. Where waters have a likelihood of containing high numbers of background microrganisms (e.g. some ambient untreated waters, effluent waters), this Standard includes the option to employ an alternative selective agar or broth (m-FC) that is generally more inhibitory and can be expected to a greater extent to restrict the number and size of background colonies. NOTES: 1 Thermotolerant coliforms are often also referred to as 'faecal coliforms' although the organisms may not be of faecal origin. 2 Membrane filtration is suitable for enumerating microorganisms only when the turbidity of the water is low. 3 A flow diagram of the procedure is shown in Appendix A.

DR 06121

AS 4276.7-1995