P3-127 Examination of Compost and Irrigation Water as On-farm Bacterial Reservoirs and Potential Contamination Routes for In-field Leafy Greens

Wednesday, July 31, 2013
Exhibit Hall (Charlotte Convention Center)
Jayde Wood, University of British Columbia, Vancouver, Canada
Elsie Friesen, BC MAL, Abbotsford, Canada
Pascal Delaquis, Agriculture and Agri-Food Canada, Summerland, Canada
Kevin Allen, University of British Columbia, Vancouver, Canada
Introduction: There is interest in developing more effective on-farm food safety interventions to reduce risks associated with fresh produce. Specifically, irrigation water and compost are significant concerns regarding the transmission of pathogenic organisms to in-field produce. 

Purpose: To determine whether populations of Escherichia coli recovered from compost and irrigation water are observed in soil and in-field leafy greens.

Methods: In-field leafy greens (n=484) and environmental samples (irrigation water, compost and soil; n = 136) were collected from two produce production systems (organic and conventional) in British Columbia weekly (July-October 2012). Coliforms and Escherichia coli counts were determined using 3M Petri-film and E. coli prevalence was evaluated by enrichment using EC broth and EMB agar. Escherichia coli isolates were subjected to BOX-PCR and multiplex PCR phylogenetic typing.  

Results: Coliform and E. coli levels on leafy greens ranged from 0.7 to 4.5 log CFU/g (mean: 1.2 ± 0.1 log CFU/g) and 0.7 to 1.6 log CFU/g (mean: 0.7 ± 0.005 log CFU/g), respectively. The overall prevalence of E. coli for leafy greens was 0.7%. Escherichia coli were recovered from the irrigation water reservoir (54%), overhead sprinkler (26%), soil (32%), and compost (6%) samples. Escherichia coli isolates belonging to four phylogenetic groups (A, B1, B2, D) were recovered from both produce production systems, with B1 being the pre-dominant phylogroup (78%). BOX-PCR revealed identical fingerprints for E. coli isolates recovered from irrigation water and in-field plants, demonstrating dissemination from the reservoir to the field. Similarly, identical strains from compost were also recovered on leafy greens. 

Significance: Levels of coliforms and E. coli recovered from in-field leafy greens were low. Despite this, BOX-PCR data highlight transmission routes and the consequent need to develop intervention strategies minimizing the transfer of potential pathogens from compost and irrigation water to in-field leafy greens.