Effect of sunlight on the survival of pathogenic E. coli in freshwater and sea water

An enteropathogenic group of E. coli are the emerging category of pathogen of public health significance. Several recent pathogenic E. coli outbreaks are associated with drinking water. Aquaculture, the fast emerging food production sector also poses a pathogenic EHEC outbreak risk, as it regularly uses cow dung, a reservoir of this organism. Hence, a experiment was set up to study the duration of survival of pathogenic E. coli under sunlight and darkness. Eight pathogenic E. coli isolates from clinical (EPEC, ETEC, EHEC, EAEC), veterinary (CTE3, CTE4) and environmental sources (ASHE3, Rao II) were studied for their survival under sunlight and darkness in fresh water and seawater. Effect of direct sunlight on the viable but nonculturable (VBNC) state of cultures was also studied. The results of the study indicated a distinct pattern between freshwater system and seawater system. Pathogenic E. coli from different sources showed significantly higher level of destruction under direct sunlight than in complete darkness. A reduction of 1.1 to 5.7 log CFU was seen in fresh water after 90 to 105 min under direct sunlight and only 0.2 to 2 log reduction was observed in complete darkness in 5 to 96 h period. The effect of sunlight was severe in seawater and in selective media, where a higher cell reduction to an extent of 3 log CFU was observed.Survival period was least for environmental pathogens followed by veterinary and finally clinical pathogens with an exception of Shiga-toxigenic E. coli (STEC) from veterinary sources. Findings of this study, may aid the public health specialist to evolve better strategies to control these organism in the above systems.