T4-08 Escherichia coli Persistence on Broccoli, Cauliflower and Chinese Cabbage Crops after Irrigation

Monday, July 23, 2012: 3:45 PM
Ballroom E (Rhode Island Convention Center)
Caroline Cote, Research and Development Institute for the Agri-Environment, Saint-Hyacinthe, Canada
Mylene Genereux, IRDA, Saint-Hyacinthe, Canada
Introduction:  Irrigation water is recognized as a potential source of human pathogens. However, few studies were conducted on the persistence of indicator microorganisms on crops after irrigation under field conditions.

Purpose:  The aim of this project was to evaluate the persistence of Escherichia coli, used as a fecal contamination indicator, on Brassicaceaecrops after irrigation with contaminated water.

Methods:  Experimental plots were set in a completely randomized design including 3 crops (broccoli, cauliflower, and Chinese cabbage) each repeated four times. Plots were spray-irrigated with water from an adjacent stream having an E. coli content of 1,151 CFU/100 ml at irrigation time. Three vegetables were sampled in each plot before irrigation and at different times after irrigation (1 hour, and 1, 2, 3, 4, 5, 6, 8, 9, 10, 19 days) for E. coli detection by enrichment and the determination of E. coli populations. A logistic regression of E. coliprevalence on time was fit to data using the SAS GLIMMIX procedure for the estimation of the equation parameters. 

Results:  E. coli could be quantified in only 5 % of the vegetables samples taken after irrigation, with bacterial contents varying between 10 and 130 CFU/g (n=396). E. coli was detected by enrichment in 28 % of the samples. Statistical analysis showed a significant impact of the crop and the delay between irrigation and harvest (and their interaction) on E. coli prevalence. The logit of E. coliprevalence decrease rates were estimated at -0.0336, -0.0114, and -0.0044 in broccoli, cauliflower and Chinese cabbage, respectively.

Significance: Results emphasize the importance of the crop and the delay between irrigation and harvest on E. coli prevalence on Brassicaceae crops.