Use of the ISO 9308-1 procedure for the detection of E. coli in water utilizing two incubation temperatures and two confirmation procedures and comparison with defined substrate technology |
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Abstract: | 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 44°C and using the defined substrate technology method Colilert-18®/Quanti-Tray® (Colilert-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 36°C. However, when glucuronidase production was used as the confirmation procedure, the confirmed count of E. coli was lowest with ISO 9308-1 performed at 36°C. When TTC medium was incubated at 36°C confirmation using production of indole at 44°C resulted in 29% more E. coli being recovered than when confirmation was performed using production of glucuronidase. When 44°C 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 44°C as the test method but °which failed to produce b-D-glucuronidase, showed that the majority of these isolates were Klebsiella oxytoca. |
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Keywords: | Colilert-18 drinking water false positive E coli ISO procedure tergitol TTC |
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