The exploration of nontraditional irrigation water sources (NTIWS) has become a national priority regarding agricultural water security due to climate variability. Therefore, sites comprising of tidal and non-tidal surface water, as well as reclaimed water were analyzed for their potential use on fresh produce as NTIWS. The Food Safety Modernization Act mandates that agricultural producers must meet stricter guidelines regarding the quality of irrigation water used on fresh produce. This study evaluated the physicochemical qualities and the presence of Shiga toxin-producing Escherichia coli (STEC) in NTIWS. The physicochemical qualities, such as temperature, dissolved O2, conductivity, pH, and, turbidity, were measured with an YSI EXO2 Multi-Parameter Water Quality Sonde. Additionally, we modified and developed a sampling apparatus to filter the water samples through a modified Moore swab. Two-hundred eighty-two samples were collected periodically, from October 2016 to November 2017, from six sites. There were 216 samples from four surface water sites (one tidal and three non-tidal) and 66 samples from two reclaimed water sites. The swabs were enriched with Universal Pre-enrichment Broth, then R&F E. coli Enrichment Broth, which was 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.
Results/Conclusions
The implementation of sampling apparatus was successful and greatly improved the efficiency of the sampling process. The non-tidal sites had 37 positive samples (37/162), which were serotypes O45 (2), O103 (1), O111 (2), and O121 (1); and virulence factors stx2 (1), ehxA (1), and eae (32). The tidal site had 9 positive samples (9/54), which were positive for serotypes O103 (1) and O111 (1); and the virulence factors stx2 (2) and eae (5). The reclaimed water sites had 6 positive samples (6/66) for the virulence factors stx1 (1), stx2 (3), eae (2). No samples were positive for E. coli O157:H7. These results indicate low prevalence of STEC in NTIWS. The outcomes of our study will be used to develop and implement next-generation on-farm water treatment technologies that can improve the quality of the NTIWS. The irrigation of fresh produce with reclaimed water will be beneficial to the ecosystem, because it could create less demand of traditional water sources and, thus reduces the amount of wastewater discharged into rivers, which negatively impacts the local aquatic environment.