Abstract
Produce has become a major source of foodborne illness, and may become contaminated through surface water irrigation. The objectives of this study were to (i) determine the frequency of verotoxigenic E. coli (VTEC), Listeria monocytogenes, and Salmonella in surface waters used for irrigation in the Lower Mainland of British Columbia, (ii) assess the suitability of fecal coliforms and generic E. coli as hygiene indicators, and (iii) investigate the correlations of environmental factors with pathogen occurrence. Water samples were collected semi-monthly for 18 months from seven irrigation ditches across the Serpentine and Sumas watersheds. VTEC colonies on water filters were detected using a verotoxin colony immunoblot, and the presence of virulence genes vt1 and vt2 was ascertained via multiplex PCR. Detection of L. monocytogenes and Salmonella was completed using standard, Health Canada Compendium of Analytical Methods. Fecal coliforms and generic E. coli were enumerated by 3M™ Petrifilm™ and filtration methods, and meteorological and geographic data were collected from government records. VTEC, L. monocytogenes, and Salmonella were detected in 4.93%, 10.3%, and 2.69% of 223 samples, respectively. L. monocytogenes occurrence was greatest in the Serpentine watershed (χ2; p < 0.05), and was most common during the winter and fall (Fisher exact test; p < 0.05). Site dependence of VTEC and Salmonella occurrence was observed within watersheds (Fisher’s exact test; p < 0.10). Pathogen occurrence correlated with fecal coliform counts (r = 0.448), while VTEC occurrence also correlated with precipitation over the five days before sampling (r = 0.239). The density of upstream livestock correlated with VTEC (rs = 0.812), and L. monocytogenes (rs = 0.841) detection. These data show that foodborne pathogens are present in the waters used for irrigation in the Lower Mainland of British Columbia, but their frequency may depend on spatial and temporal factors.
Highlights
Foodborne illness continues to be an issue for consumers
The recovery of pathogens was more common in the Serpentine watershed compared to the Sumas watershed, with 22.3% compared to 10.9% occurrence, respectively (χ2; p = 0.032). This difference was primarily due to the increased occurrence of L. monocytogenes observed in the Serpentine watershed compared to the Sumas watershed: 18.1% and 4.65%, respectively (χ2; p = 0.002)
No significant sitespecific differences were observed for L. monocytogenes in either watershed, though two thirds of positive samples from the Sumas watershed came from a single site
Summary
In addition to health costs, foodborne illnesses can lead to an economic burden due to lost productivity and wages among those affected [1]. Though foodborne pathogens, such as Listeria monocytogenes, Salmonella, and verotoxigenic Escherichia coli (VTEC), are generally associated with meat and dairy products, produce has been observed to be a major source of foodborne illness: produce accounted for more foodborne illnesses and outbreaks than any other food category in the United States between 2004 and 2013 [2], and led to 27 outbreaks in Canada between 2001 and 2009 [3]. The bacteria are able to survive for long periods, and may not to be removed through washing [12], leading to considerable risks associated with any produce consumed raw, such as leafy greens and sprouts
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