P3-39 Examination of Irrigation Water as an On-farm Bacterial Reservoir and Potential Contamination Route for In-field Leafy Greens

Wednesday, July 25, 2012
Exhibit Hall (Rhode Island Convention Center)
Jayde Wood, University of British Columbia, Vancouver, Canada
Kevin Allen, University of British Columbia, Vancouver, Canada
Elsie Friesen, BC MAL, Abbotsford, Canada
Introduction: In the production of produce, irrigation water quality has been a primary concern for the produce industry. Despite this, the causal relationship between irrigation water quality and produce safety is not well understood.

Purpose: To examine how poor and high quality irrigation water influences the microbiological quality of in-field leafy greens grown in a conventional production system.

Methods: Pre-harvest plant (n=279) and irrigation water samples from two sources (municipal water [n=9] and ditch water [n=19]) were collected from a conventional farm production system in British Columbia (BC), Canada, weekly between August and October 2011. Levels of coliforms and Escherichia coli were determined using 3M Petri-Films. Recovered E. coli isolates were subjected to antibiogram typing and phylogenetic multiplex PCR analysis. 

Results: Levels of coliforms on leafy greens ranged from 0.7 to 2.0 log CFU/g, with an average of 1.2 ± 0.1 log CFU/g. No E. coli isolates were recovered from leafy greens irrigated with municipal water whilst one sample of 149 (0.7%) irrigated with ditch water tested positive. While no coliforms were detected in municipally treated water, coliforms and E. coli were detected in 19/19 ditch water samples, with average levels of coliforms and E. coli of 4.1 ± 0.2 log CFU/100ml and 2.7 ± 0.3 log CFU/100ml observed, respectively. E. coli isolates belonging to all four phylogroups (A, B1, B2, D) were detected in ditch water.

Significance: Regardless of whether in-field produce was irrigated with ditch or municipal-quality water, the levels and frequency of coliforms and E. coli recovery was low. Further, the low incidence of E. coli observed in produce irrigated with poor quality water suggests undefined factors may impair E. coli’s ability to survive following transition from an aqueous milieu to the plant biosphere.