Disinfected and non-disinfected samples have been used to determine the accuracy of the ISO procedure (ISO 9308-1) for detection of E. coli in drinking water. Samples were analysed using the ISO procedure at both 36 and 448C and using the defined substrate technology method -18). Utilizing the confirmation procedure described in ISO 9308-1, large numbers of false positive E. coli results were obtained using the ISO primary isolation procedure at 368C. However, when glucuronidase production was used as the confirmation procedure, the 'confirmed' count of E. coli was lowest with ISO 9308-1 performed at 368C. When TTC medium was incubated at 368C confirmation using production of indole at 448C resulted in 29% more 'E. coli' being recovered than when confirmation was performed using production of glucuronidase. When 448C was used as the primary isolation temperature the difference between the number of 'confirmed' E. coli identified using the two confirmation procedures was less than 1% and was not significant. Identification of isolates which 'confirmed' when using production of indole at 448C as the test method but 8which failed to produce b-D-glucuronidase, showed that the majority of these isolates were Klebsiella oxytoca.
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