Association of nuisance filamentous algae Cladophora spp. with E. coli and Salmonella in public beach waters: impacts of UV protection on bacterial survival.

This study investigated whether filamentous algal species commonly found in nearshore public beach water systems provide protection from natural UV to bacteria present in the same environmental settings. To test this hypothesis, Cladophora spp., a filamentous nuisance algae group causing undesired water quality in the Great Lakes region was selected and its interactions with a non-pathogenic indicator organism Escherichia coli and a pathogenic strain of Salmonella enterica serovar Typhimurium were tested. In laboratory microcosms where the lake environment and natural sunlight conditions were simulated, a 7-log removal of E. coli was observed in only six hours of exposure to UV with an initial seed concentration of 10(3) CFU mL(-1). With the presence of algae, the same log removal was achieved in 16 hours. At higher seed concentrations of 10(5) CFU mL(-1), E. coli survived for two days with an extended survival up to 11 days in the presence of Cladophora spp. S. typhimurium has shown more resilient survival profiles, with the same log removals achieved in 14 and 20 days for low and high seed concentrations respectively, in the absence of algae. Cladophora spp. caused extended protection for S. typhimurium with much less log reductions reported. Algae-mediated protection from UV irradiation was attributed to certain organic carbon exuded from Cladophora spp. In addition, confocal microscopy images confirmed close interaction between bacteria and algae, more prominent with thin filamentous Cladophora spp.