Purpose: The purpose of this study is to determine populations of indicator organisms and the presence of Salmonella and Shiga Toxin-producing Escherichia coli (STEC) genes in agricultural water.
Methods: Water samples (500 ml) from six agricultural ponds were collected during the 2012/2013 and 2013/2014 growing seasons (46 and 44 samples, respectively, 540 total). Microbial indicator populations (total coliforms, generic Escherichia coli, and Enterococci) were enumerated. A microbial water quality profile (WQP) was established for all ponds. Water (150 ml) was filtered and filters stored at -20°C until pathogen analysis by PCR. For STEC, filters were enriched in modified buffered peptone water with pyruvate at 35 ± 2°C for 24 h, DNA extracted, and multiplex PCR for detection of six genes (hly, fliC, eaeA, rfbE, stx-I, and stx-II), run. For Salmonella, the presence of the invA gene was evaluated following a subsequent enrichment in Rappaport-Vassiliadis 42 ± 1°C for 48 h and DNA extraction.
Results: All ponds met the current FDA WQP recommendations 100.0% of the time. All STEC genes were detected in 2.6% of the samples. Individual STEC genes varied in the number of samples they were detected in: hly-83.3%, fliC-51.8%, eaeA-17.4%, rfbE-17.4%, stx-I-32.6% stx-II-9.4%. The invA gene was detected in 26/540 (4.8 %) samples, in all ponds and both growing seasons. However, 57.7 % (15/26) of the invA positive samples were from ponds 2 and 4, where the WQP was the poorest.
Significance: Surface waters tested in Central Florida meet the FDA recommendations for microbial water quality, however at least one Salmonella or STEC gene was detected in 91.3% of samples. Understanding the relationships between indicator microorganisms and pathogens presence allows a greater understanding of agricultural water risks.