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 host-specific 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 ruminant-specific 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 (R-2 = 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.