Sunlight inactivation of Campylobacter jejuni and Salmonella enterica, compared with Escherichia coli, in seawater and river water

The inactivation of Campylobacter jejuni and Salmonella enterica, compared with Escherichia coli, was determined in 100 l chambers of seawater and river water located at an outdoor site. The chambers (paired with dark controls) were seeded with waste stabilization pond effluent and laboratory-cultured pathogens, and exposed to sunlight in summer and winter experiments. All sunlight inactivation (k_S) rates, as a function of cumulative global solar radiation (insolation), were far higher than the corresponding dark (k_D) rates, with a ranking (and average k_S rates for seawater and river water, respectively) of: C. jejuni (3.23; 2.34)>S. enterica (0.51; 0.37)>E. coli (0.34; 0.26). All the T₉₀ (time to 90% inactivation) values were higher in winter than in summer, but there was far greater similarity between the summer and winter S₉₀ (insolation needed for 90% inactivation) values. The rapid inactivation of C. jejuni was attributed to a high susceptibility to photooxidative damage. The results suggest that, in sunlight-exposed waters, E. coli will be a more conservative indicator for C. jejuni than for S. enterica, and C. jejuni transmission as a pathogenic agent is less likely than for S. enterica.