Impact of storm runoff onSalmonellaandEscherichia coliprevalence in irrigation ponds of fresh produce farms in southern Georgia

Abstract

Aims: To examine Salmonella and Escherichia coli in storm runoff and irrigation ponds used by fresh produce growers, and compare Salmonella serovars with those found in cases of human salmonellosis. Methods and Results: We collected water before and after rain events at two irrigation ponds on farms in southern Georgia, USA, and collected storm runoff/storm flow within the contributing watershed of each pond. Salmonella and E. coli concentrations were higher in ponds after rain events by an average of 0.46 (P < 0.01) and 0.61 (P < 0.05) log10 most probable number (MPN) 100 ml−1, respectively. Salmonella concentrations in storm runoff from fields and forests were not significantly higher than in ponds before rain events, but concentrations in storm flow from streams and ditches were higher by an average of 1.22 log10 MPN 100 ml−1 (P < 0.001). Eighteen Salmonella serovars were identified from 155 serotyped isolates, and eight serovars were shared between storm runoff/storm flow and ponds. Seven of the serovars, including five of the shared serovars, were present in cases of human illness in the study region in the same year. However, several serovars most commonly associated with human illness in the study region (e.g. Javiana, Enteritidis, and Montevideo) were not found in any water samples. Conclusions: Salmonella and E. coli concentrations in irrigation ponds were higher, on average, after rain events, but concentrations of Salmonella were low, and the ponds met FDA water quality standards based on E. coli. Some similarities and notable differences were found between Salmonella serovars in water samples and in cases of human illness. Significance and Impact of Study: This study directly examined storm runoff/storm flow into irrigation ponds and quantified increases in Salmonella and E. coli following rain events, with potential implications for irrigation pond management as well as human health.

Prevalence of Salmonella and Listeria monocytogenes in non-traditional irrigation waters in the Mid-Atlantic United States is affected by water type, season, and recovery method

“…This analysis is in agreement with previous studies which have shown poor correlation between the ability of physicochemical factors to influence levels of S. enterica in river waters in Florida [26]. Other authors have shown that Salmonella levels in ponds are not correlated to total suspended solids (TSS) before or after rainfall events [27]. Prevalence rates of Salmonella (50%) and L. monocytogenes (31%) in the current study are greater than those reported for STEC (2.35%) using several of the same sampling dates and sites [19].…”

Landscape, Water Quality, and Weather Factors Associated With an Increased Likelihood of Foodborne Pathogen Contamination of New York Streams Used to Source Water for Produce Production

“…(excluding monocytogenes), and L. monocytogenes detection. Overall, these findings are not unexpected since past studies have found associations between "hydrological" factors and pathogen isolation (e.g., Goyal et al, 1977;Baudart et al, 2000;Kistemann et al, 2002;Cooley et al, 2007;Haley et al, 2009;Wilkes et al, 2009Wilkes et al, , 2011Walters et al, 2011;Luo et al, 2015;Harris et al, 2018). A study that examined associations between environmental factors and pathogen isolation from Ontario river water only detected Salmonella when surface water discharge rates were elevated, which led the authors to conclude that events that promote off-farm and in-stream transfer of microbes (e.g., rain events) must occur for detection of Salmonella in the sampled rivers (Wilkes et al, 2011).…”

Factors Impacting the Prevalence of Foodborne Pathogens in Agricultural Water Sources in the Southeastern United States

“…In a study conducted in southeast Georgia, the presence of E. coli O157:H7 was positively correlated with the concentration of fecal coliforms, but not generic E. coli, suggesting that a single indicator may not be adequate to assess the microbiological quality of irrigation water [50]. In addition, previous studies have demonstrated that generic E. coli does not correlate well with Salmonella [49,[51][52][53], Campylobacter spp. [54], and E. coli O157:H7 [53,55] presence.…”

“…In another study conducted in the same area, water samples were collected from irrigation ponds (near the intake source), storm runoff from forest, and storm flow from ditches and streams to determine the incidence of Salmonella and E. coli contamination in irrigation ponds on fresh produce farms before and after twelve rain events. Results demonstrated that Salmonella and generic E. coli levels were significantly higher after rainfall events in water samples from the ponds and lower in storm runoff from forests [51]. Also, Salmonella was isolated from 100% of samples collected from storm flow in streams and ditches, suggesting that recharging streams were the possible source of Salmonella in the irrigation ponds after precipitation instead of runoff from forests [51].…”

“…Results demonstrated that Salmonella and generic E. coli levels were significantly higher after rainfall events in water samples from the ponds and lower in storm runoff from forests [51]. Also, Salmonella was isolated from 100% of samples collected from storm flow in streams and ditches, suggesting that recharging streams were the possible source of Salmonella in the irrigation ponds after precipitation instead of runoff from forests [51]. In another study, the concentration of C. jejuni were positively correlated to rainfall events with an average prevalence of 58% in water samples collected from six sites along the Satilla River basin in southeast Georgia [67].…”