Purpose: Our objective is to improve current knowledge of factors and indicators associated with the occurrence of verotoxigenic E. coli (VTEC), Salmonella, and Listeria monocytogenes in irrigation water used in the Lower Mainland of British Columbia, Canada.
Methods: Water samples were collected bi-monthly between March and December 2015 from up to seven irrigation ditches in the Serpentine and Sumas watersheds of BC. VTEC colonies on water filters were detected using a verotoxin colony immunoblot (VT-IB) developed for the detection of all VTEC serotypes, and isolates were confirmed via multiplex PCR for virulence genes stx1 and stx2. Detection of Salmonella and L. monocytogenes was completed using Health Canada Methods. Generic E. coli were enumerated using 3M Petrifilm Count Plates, and meteorological data were collected from Environment Canada records.
Results: VTEC, Salmonella, and L. monocytogenes were detected in 3 (2.7%), 3 (2.7%), and 14 (12.5%) of 112 samples, respectively. Pathogen occurrence was greater in the Serpentine watershed compared to the Sumas watershed (χ2, P = 0.04), with L. monocytogenes also suggesting an increased occurrence in the Serpentine watershed (Χ2, P = 0.07). Pathogen occurrence also correlated with lower temperatures (rpb = -0.37), with positive samples being collected primarily during spring and fall. The number of generic E. coli correlated with the presence of both VTEC (rpb = 0.538) and L. monocytogenes (rpb = 0.442), but not with Salmonella. No correlations with precipitation were observed.
Significance: This research adds to the continued work to develop accurate risk models for these three pathogens, and may lead to economically feasible solutions for risk reduction at the farm level.