Investigation of Escherichia coli in Urban Steam with Inflow of Treated Wastewater

Abstract

There is growing concern for the applicability of Escherichia coli as a fecal indicator bacterium in the water environment because E. coli has been reported to regrow in a variety of environments. We investigated longitudinal variation in E. coli counts along a small channel which receives the effluent of treated wastewater. The two fecal indicator bacteria, E. coli and Enterococci, were enumerated, and these bacterial fluxes were calculated from bacteria counts and river flow. As a result, the flux of E. coli was larger downstream of the effluent site than the sum of the fluxes upstream and in the effluent. A high E. coli count was detected in the riverbed sediment of a downstream site. In addition, pulsed-field gel electrophoresis revealed that the genotypes of E. coli isolated from the upstream water, periphyton, and riverbed sediment samples were concordant (similarity = 1.0) . These results indicate that E. coli survived and accumulated in riverbed periphyton and sediment and that E. coli may regrow in a small stream that is strongly affected by treated wastewater. When we assess the fecal pollution in rivers, it is necessary to consider the possibility of E. coli regrowth.