Performance characteristics of the temperature-modified ISO 9308-1 method for the enumeration of Escherichia coli in marine and inland bathing waters.

Abstract This study defines performance characteristics of the temperature-modified ISO 9308-1 method for E. coli enumeration in bathing water. After a 4-hour resuscitation period at 36 ± 2 °C, the incubation temperature was changed to 44 ± 0.5 °C. Elevated incubation temperature significantly suppressed the growth of thermo-intolerant bacteria, and enhanced the selectivity of Chromogenic Coliform Agar (CCA) up to 49.5% for inland and up to 66.0% for coastal water. Consequently, most of the selectivity-related performance characteristics are improved. Relative recovery was determined by comparing an alternative method against the reference, ISO 9308-1:2014 method, following the criteria set out in ISO 17994:2014. Temperature modification did not significantly alter the results and the methods were evaluated as "not different" for both, coastal and inland waters. Chromogenic Coliform Agar was assessed as a suitable medium for reliable E. coli enumeration in bathing water when incubated for 17–19 h at 44 ± 0.5 °C after the 4–5 h resuscitation period at 36 ± 2 °C. Graphical abstract Unlabelled Image Highlights • A resuscitation period was crucial for E. coli recovery by the modified method. • Relative recovery was high for both inland and coastal bathing water samples. • Temperature modification significantly enhanced the selectivity of the method. • All performance characteristics meet the requirements of ISO 13843:2017. • The method was assessed as suitable for E. coli enumeration in bathing water. [ABSTRACT FROM AUTHOR]

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