Methods for enumeratingEscherichia coliin subtropical waters

Abstract

SUMMARYThe standard membrane filtration method of the UK has been modified in order to improve its specificity for enumeratingEscherichia coliin the subtropical waters of Hong Kong. This involves incorporating into the membrane lauryl sulphate (mLS) method either anin situurease test (the mLS-UA method), or anin situβ-glucuronidase test (the mLS-GUD method). The false-positive errors of the mLS-UA and mLS-GUD methods are low, ranging from 3–5%. A comparison between the membrane filtration (mLS-UA) method and the multiple tube technique in testingE. coliin subtropical beach-waters has demonstrated that the former can give much more precise counts, and is the method of choice for such a purpose. The mLS-GUD method, for which automated counting ofE. colicolonies is possible, is a good alternative to mLS-UA in routine enumeration of this bacterial indicator in environmental waters.