P3-128 Comparative Transmission from Contaminated Irrigation Water on Field-grown Spinach and Lettuce

Wednesday, July 31, 2013
Exhibit Hall (Charlotte Convention Center)
Rachel Brown, University of Delaware, Newark, DE
Patrick Spanninger, University of Delaware, Newark, DE
Krystal Shortlidge, University of Delaware, Newark, DE
Angela Marie Ferelli, University of Delaware, Newark, DE
Kalmia Kniel, University of Delaware, Newark, DE
Introduction: An essential issue of GAPs is the use of low-risk irrigation water to reduce contamination of pathogens onto produce. The metrics to define low-risk remain undefined, in particular for leafy greens.

Purpose: To compare bacterial persistence on lettuce and spinach grown in the mid-Atlantic region following a one-time contamination event with water contaminated with varying amounts of coliforms originating from bovine manure.

Methods: Parris Island Romaine lettuce and Melody hybrid spinach plants (n = 388) were irrigated overhead with water containing varying levels of coliforms (0, 100, 1000 and 10000 CFU/ml each in 3 plots). Samples were randomly collected at days 0, 0+ (immediately following inoculation), 1, 3, 5, 7 and 10. One sample was composed of three randomly chosen 28-day old plants for each leafy green. Total coliforms (37°C), fecal coliforms (44.5°C), and Escherichia coli were detected using bacterial enumeration on TBX media and MPN using colilert methods. 

Results: Log MPN counts were significantly lower on Days 0 and 0+ compared to all other days (P < 0.0001) for both produce types. After day 7 counts were significantly higher (P < 0.0001) in relation to all other days and the highest on day 10 (log MPN/g = 6.56+/- 0.11), specifically associated with a spinach sample from 10000 CFU/ml. By day 10, the fields had received > 6 cm of water during a hurricane, which showed an increase in total coliform count but had a diminishing effect on fecal coliform count. Coliform levels from TBX, incubated at 44.5°C, indicated higher levels from days 1-5 at 20,000 CFU/g on lettuce and 1500 CFU/g on spinach associated with higher inoculation levels. E. coli levels did not differ significantly on lettuce or spinach.

Significance: These data suggest that monitoring irrigation water and the use of field trials to simulate pre-harvest contamination effects will enhance our understanding of irrigation water metrics and meteorological effects.