Ambient-temperature incubation for the field detection ofEscherichia coliin drinking water

Abstract

Aims: Escherichia coli is the pre-eminent microbiological indicator used to assess safety of drinking water globally. The cost and equipment requirements for processing samples by standard methods may limit the scale of water quality testing in technologically less developed countries and other resource-limited settings, however. We evaluate here the use of ambient-temperature incubation in detection of E. coli in drinking water samples as a potential cost-saving and convenience measure with applications in regions with high (>25°C) mean ambient temperatures. Methods and Results: This study includes data from three separate water quality assessments: two in Cambodia and one in the Dominican Republic. Field samples of household drinking water were processed in duplicate by membrane filtration (Cambodia), Petrifilm™ (Cambodia) or Colilert® (Dominican Republic) on selective media at both standard incubation temperature (35–37°C) and ambient temperature, using up to three dilutions and three replicates at each dilution. Matched sample sets were well correlated with 80% of samples (n = 1037) within risk-based microbial count strata (E. coli CFU 100 ml−1 counts of <1, 1–10, 11–100, 101–1000, >1000), and a pooled coefficient of variation of 17% (95% CI 15–20%) for paired sample sets across all methods. Conclusions: These results suggest that ambient-temperature incubation of E. coli in at least some settings may yield sufficiently robust data for water safety monitoring where laboratory or incubator access is limited. Significance and Impact of the Study: Ambient-temperature incubation of E. coli may be a promising option for reducing the complexity and costs associated with water safety monitoring for faecal indicator bacteria such as E. coli in a field context in resource-limited settings, as are often encountered in developing countries and after disasters.