Purpose: This study examined whether the current E. coli standards were associated with pathogen presence in irrigation water. We then evaluated the utility of E. coli, other traditional fecal indicator microorganisms, and molecular microbial source tracking (MST) markers as tools for predicting the presence of pathogens.
Methods: Irrigation water was collected from three ponds in a southern Georgia growing region over one year. Samples were analyzed for Salmonella and fecal indicators E. coli, enterococci, and male-specific bacteriophages. Samples were also analyzed for MST markers of fecal contamination including: human, avian, ruminant, pig, and chicken specific targets. Logistic and linear regression were conducted to compare detection rates and concentrations of Salmonellaand indicators.
Results: Salmonella presence was not associated with E. coli concentrations above the USEPA recreational water geometric mean standard of 126 MPN/100 mL or the statistical threshold value of 410 MPN/100 mL. There were no associations between the presence of any indicator to Salmonella presence. However, E. coli and enterococci concentrations were positively associated with Salmonella presence. E. coli, enterococci, and bacteriophage concentrations were also positively correlated with Salmonella concentration. The MST markers were not associated with Salmonellapresence or concentration.
Significance: Our results show that recreational water quality standards for E. coli were not predictive of Salmonella presence in the irrigation ponds studied in southern Georgia. Further research is needed to evaluate E. coli guideline values and consider alternative agricultural water quality indicators.