Evaluating Non-Traditional Irrigation Water Sources for the Presence of Shiga Toxin-Producing Escherichia coli in the US Mid-Atlantic Region.

The exploration of nontraditional irrigation water sources (NTIWS) has become a national priority with regard to agricultural water security because of climate variability. The NTIWS that are being analyzed for potential use on fresh produce are tidal and non-tidal surface water as well as reclaimed water. As a result of the Food Safety Modernization Act, agricultural producers must meet stricter guidelines regarding the quality of irrigation water used on fresh produce. We are evaluating the physicochemical qualities of NTIWS and for Shiga-toxin producing Escherichia coli (STEC). In this study, we measured the physicochemical qualities (temperature, dissolved O₂, conductivity, pH, turbidity, and other parameters) using a YSI EXO2 Multi-Parameter Water Quality Sonde. We also modified and developed a sampling apparatus that was used to filter the water samples through a modified Moore swab; which has the potential of greatly improving the sampling process of surface and reclaimed waters for bacterial detection. One-hundred thirty-eight samples were collected periodically starting fall 2016 into summer of 2017 from six sites; where 108 samples were from four surface water sites (one tidal and three non-tidal) and 30 samples were from two reclaimed water sites. The swabs were enriched, then streaked on both R&F Non-O157 STEC Chromogenic plating medium and CHROMagar O157. Presumptive STEC colonies were confirmed using an 11-plex traditional PCR. The non-tidal sites had 13 positive samples (13/81), which were serotypes O45 (1), O111 (2), and O121 (1), and virulence factors stx₂ (2) and eae (8). The tidal site had one positive sample (1/27) for both serotype O111 and the virulence factor eae. There was one positive sample (1/30) from the reclaimed water sites for the virulence factor eae. No samples were positive for O157. These results indicate low prevalence of STEC in NTIWS.

. Sampling is ongoing and will continue for an additional three years.