Evaluating the occurrence of host-specific bacteroidales, general fecal indicators, and bacterial pathogens in a mixed-use watershed

Fecal contamination of water is very common, and, in the United States, prevention is complicated by the colossal span of waterways (>3.5 million miles), heterogeneous sources of pollution, and competing interests in water monitoring. The focus of this study was the Upper Sugar Creek Watershed, a mixed-use watershed with many headwater streams and one of the most contaminated waterways in Ohio. Quantitative polymerase chain reaction (qPCR) and hostspecific PCR for Bacteroidales were evaluated for the potential to discern sources of fecal contamination. Pathogen-specific qPCR and culturable Escherichia coli by most probable number (MPN) were compared at 21 established water quality monitoring sites in the watershed headwaters. Lower numbers of ruminantspecific Bacteroidales markers were detected in the base flow water samples compared with the human-specific Bacteroidales marker, suggesting the presence of hotspots of human fecal contamination. Bacteroidales qPCR and E. coli MPN showed significant correlation (R2 = 0.57; P < 0.001). Correlation between general fecal indicator and pathogen concentrations was weak or nonexistent. Coexistence of Salmonella and human-specific Bacteroidales was common (P = 0.015). Bacteroidales qPCR may have a greater potential for predicting fecal contamination due to its sensitivity, rapid analysis, and availability of host-specific assays. However, the lack of a strong correlation between pathogens and general fecal indicators suggests that assessment of health risk associated with fecal contamination will require a complement of approaches.