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Occurrence and potential predictors of verotoxigenic Escherichia coli (VTEC), Salmonella, and Listeria monocytogenes in surface water used for produce irrigation in the Lower Mainland of British Columbia, Canada

University of British Columbia

Foodborne pathogens such as verotoxigenic Escherichia coli (VTEC), Salmonella, and Listeria monocytogenes may be present in surface waters, thus having the potential to contaminate fresh produce during crop irrigation. The objectives of this study were to determine the occurrence of VTEC, Salmonella, and L. monocytogenes in surface waters used for produce irrigation in the Lower Mainland of British Columbia, and to investigate potential predictors of their presence. Water samples (n = 223) were collected from three and four irrigation ditches in both the Serpentine and Sumas watersheds, respectively, between February 2015 and August 2016. VTEC colonies on water filters were detected using a verotoxin colony immunoblot developed for the detection of all VTEC serotypes, and isolates were confirmed via multiplex PCR for virulence genes vt1 and vt2. Detection of Salmonella and L. monocytogenes was completed using Health Canada Methods MFHPB-20 and MFHPB-30, respectively. Generic E. coli (EC) and fecal coliforms (FC) were enumerated using 3M™ Petrifilm™ Count Plates, and by membrane filtration with growth on m-FC agar with 0.01% rosalic acid; this was followed by transfer to nutrient agar containing 4-methylumbelliferyl-β-D-glucuronide. Meteorological data were collected from Environment Canada records, and agricultural data were collected from the British Columbia Agricultural Land Use Inventories. The most commonly occurring pathogen was L. monocytogenes (11.2%), followed by VTEC (4.93%), and Salmonella (2.68%). Pathogen recovery was more common in the Serpentine watershed (p < 0.05), especially during the winter and fall seasons (p < 0.05). Pathogen occurrence in these locations was correlated with FC (r = 0.431) and EC (r = 0.408), but only by using the membrane filtration method. Pathogens were still recovered when indicator concentrations were low. Pathogen occurrence was also correlated with the proximity to upstream livestock (rs = -0.886) and the level of precipitation the day before sample collection (r = 0.203). In conclusion, VTEC, Salmonella, and L. monocytogenes are present in surface waters used for irrigation in the Lower Mainland of British Columbia. There is potential to predict their presence, but further research is required to confirm factors affecting pathogen occurrence, which entail longer sampling times and increased sampling locations.

Text

2017-04-03

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/61089

Food Science

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/