The effects of produce type on the concentration and prevalence of microbial contamination of Mexican produce and associated irrigation water Open Access

Gu, Lily (2014)

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Foodborne illnesses caused by the consumption of raw contaminated produce represent a significant public health burden. Knowledge regarding how crop type affects contamination is essential to the development of produce-specific intervention strategies to reduce or prevent contamination on the farm. This study investigates the effects of produce type on the concentration and prevalence of fecal contamination by quantifying microbial indicators of fecal contamination (fecal coliforms, E. coli, Enterococcus spp., somatic coliphage) on tomatoes, jalapeño peppers, and cantaloupes throughout farm production, as well as in associated surface drip irrigation water from 11 farms in northern Mexico. During the 2011-2012 growing seasons, whole fruit rinses of produce (n=254) were collected during pre-harvest, harvest, distribution, and packing. Water samples (n=76) were collected pre-harvest from the irrigation distribution lines as close as possible to sampled produce. Among produce combined from all production stages, cantaloupes had significantly higher microbial concentrations and were approximately three and over 30 times more likely to be positive for E. coli and Enterococcus, respectively, compared with other crop types. At each production stage, cantaloupes also had significantly higher microbial concentrations compared with at least one other crop type as well as had higher prevalence of E. coli and Enterococcus at all production stages except packing. Tomato associated irrigation water had significantly higher E. coli concentrations compared with jalapeño and cantaloupe associated water, and was approximately nine and five times more likely to be positive for E. coli than were jalapeño and cantaloupe associated water, respectively. Tomato associated water was also over nine times more likely to be positive for somatic coliphage than was cantaloupe associated water. Pre-harvest produce and associated irrigation water were not found to be related in terms of microbial contamination. In general, all produce types had microbial contamination pre-harvest, and both concentrations and prevalence did not differ across the production stages. Because microbial contamination generally did not change from pre-harvest to packing, we recommend the implementation of practices to reduce risk of produce contamination, especially cantaloupe contamination, during pre-harvest.

Table of Contents


Background and importance...1

Produce contamination on the farm...2

Irrigation water and produce contamination...3

Quantification of produce and water contamination...3

Research goal...5


Sample collection...6

Microbial analysis...7

Microbial quantification...8

Statistical analysis...9


Descriptive statistics...13

Comparisons of microbial concentrations...13

Comparisons of microbial prevalence...17

Microbial contamination on produce through farm production...19

Correlations and associations between pre-harvest produce and irrigation water...19

Power analysis...20


Cantaloupes have greater contamination...22

Proposed mechanisms...23


Tomato associated irrigation water has greater contamination...30

Proposed mechanisms...31


Recommendations for farms...34

Strengths and limitations...35

Future research...36


Tables & Figures...45

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