Effect of oxygen on survival of faecal pollution indicators in drinking water

Aims: The aim of this study was to determine the effect of oxygen on the survival of faecal pollution indicators including Escherichia coli in nondisinfected drinking water. Methods and Results: Aerobic and anaerobic drinking water microcosms were inoculated with E. colt ATCC 25922 or raw sewage. Survival of E. colt was monitored by membrane filtration combined with cultivation on standard media, and by in situ hybridization with 16S rRNA-targeted fluorescent oligonucleotide probes. Anaerobic conditions significantly increased the survival of E. colt in drinking water compared with aerobic conditions. Escherichia coli ATCC 25922 showed a biphasic decrease in survival under aerobic conditions with an initial first-order decay rate of -0.11 day(-1) followed by a more rapid rate of -0.35 day(-1). In contrast, the first-order decay rate under anaerobic conditions was only -0.02 day(-1). After 35 days, <0.01% of the initial E. coli ATCC 25922 population remained detectable in aerobic microcosms compared with 48% in anaerobic microcosms. A poor survival was observed under aerobic conditions regardless of whether E. coli ATCC 25922 or sewage-derived E. coli was examined, and regardless of the detection method used (CFU or fluorescent in situ hybridization). Aerobic conditions in drinking water also appeared to decrease the survival of faecal enterococci, somatic coliphages and coliforms other than E. colt. Conclusions: The results indicate that oxygen is a major regulator of the survival of E. colt in nondisinfected drinking water. The results also suggest that faecal pollution indicators other than E. colt may persist longer in drinking water under anaerobic conditions. Significance and Impact of the Study: The effect of oxygen should be considered when evaluating the survival potential of enteric pathogens in oligotrophic environments.