Purpose: This study evaluated the prevalence, concentration, and diversity of Salmonella in agricultural surface water used in pre-harvest production.
Methods: Twenty agricultural ponds were sampled during the 2015 and 2016 growing seasons. A total of 400 water samples (250 mL) were cultured for Salmonella using standard methods. One representative isolate from each Salmonella-positive water sample was serotyped by the National Veterinary Services Laboratories. In 2016, a three-by-three tube MPN was used to estimate the concentration of Salmonella in each sample. Additionally, environmental and meteorological factors were analyzed for their association with the detection of a Salmonella-positive water sample using logistic regression analysis.
Results: Salmonella was detected in 19% of water samples in each year (38/200; 2015 and 38/200; 2016). For 2016, the average concentration of Salmonella was 0.10 MPN/mL, with a standard deviation of 0.16 MPN/mL. The highest concentration of Salmonella was 0.93 MPN/mL (n=1); however, 79% (158/200) of samples were below the limit of detection (0.03 MPN/mL). Of the 38 isolates sent for serotyping in 2015, nine different serovars were identified including Newport, Javiana, Berta, Norwich, Saintpaul, Thompson, Infantis, Senftenberg, and Typhimurium. Interestingly, 50% of the serovars were Salmonella Newport (n=19). Furthermore, precipitation on the day of or prior to sampling and pond location significantly increased the likelihood of detecting Salmonella (P< 0.05).
Significance: Volume of water tested had an impact on the probability of detecting Salmonella in water samples. While the prevalence of Salmonella was high, the concentration was extremely low and may not pose a public health risk, especially if water is not applied to the harvestable portion of the crop.