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Examination of microbiological quality of in-field leafy vegetables and identification of on-farm generic Escherichia coli transmission dynamics

University of British Columbia

Fresh produce has increasingly been linked to foodborne outbreaks in North America. Although contamination of produce may occur at any point along the food continuum, significant risks are thought to occur at the farm level. Data illustrating bacterial transmission dynamics on farm, however, are lacking. The aim of this project was to produce baseline data describing the occurrence of indicator bacteria on in-field leafy vegetables; examine antimicrobial resistance (AMR) of recovered Escherichia coli; and identify on-farm microbiological reservoirs impacting leafy vegetables. In-field plants (n=1093) and environmental samples (irrigation water, compost, soil, and hand swabs; n=316) were collected from two production systems (conventional and organic) weekly between July-October during 2011 and 2012. Aerobic colony, coliform, and Escherichia coli counts were determined using 3M Petri-films. Escherichia coli prevalence was determined by enrichment with recovered isolates subjected to BOX-PCR and multiplex PCR phylogenetic typing. Mean coliform count for in-field plants was 1.2 ± 0.1 log₁₀ CFU/g. The prevalence of E. coli was 0.8 and 7% for conventional and organic leafy vegetable samples, respectively. No AMR to therapeutically critical antibiotics was observed in E. coli recovered from in-field plants, though nine (13%, n=67) multi-drug resistant strains were identified. Escherichia coli was recovered from an irrigation water reservoir (27%, n = 15), sprinkler (40%, n = 35), soil (58%, n = 19), hand swabs (4%, n = 27), and compost (6%, n = 16) from the organic production system. Escherichia coli was recovered from ditch water (100%, n = 10), and soil (12%, n = 25) from the conventional production system. Four phylogenetic groups were recovered, with B1 E. coli being the predominant phylogroup (78%). Though 92% of recovered E. coli were unrelated, BOX-PCR revealed identical fingerprints for E. coli recovered from irrigation water or compost and in-field plants. In summary, based on E. coli levels (n=5, c=2, m=100 CFU/g, M=1,000 CFU/g), the microbiological quality of leafy vegetables from both farms was acceptable. BOX-PCR data demonstrated transmission of E. coli from on-farm reservoirs to in-field plants, suggesting possible transmission routes for foodborne pathogens. The limitation of B1 E. coli as fecal indicators was highlighted.

Text

2013-06-28

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/44613

Food Science

University of British Columbia

UBCV

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