Assessing microbial contamination on produce, environmental sources, and farm worker hands throughout the production process on farms and packing sheds in northern Mexico Open Access

Lickness, Jacquelyn (2014)

Permanent URL:


Produce-related foodborne illnesses are a significant public health burden. It is critical to identify routes of fecally-associated contamination in produce in the agricultural production environment to design appropriate interventions aimed at preventing the introduction of microbial contamination on farms. The study goals were to quantify microbial contamination in soil, water, hand rinse, and produce rinse samples for four microbial indicators (E. coli, Enterococcus spp., fecal coliforms, and somatic coliphages) and to assess the relationship between microbial contamination in produce rinses and soil, water, and hand rinse samples. Produce rinse samples (N=279) were collected from farms and packing sheds and matched to soil (N=81), water (N=164) and hand rinse samples (N=196) during the 2011 and 2012 growing seasons. Samples were processed by enumerative methods for E. coli, Enterococcus spp., fecal coliforms, and somatic coliphages. We used bivariate analysis, multivariate linear models, and logistic models to evaluate the relationship between produce rinse samples and environmental samples for all four microbial indicators. Our findings showed low levels of contamination in soil and water samples and a lack of association between soil and water contamination and produce contamination. We also found a high proportion of positive samples in hand rinses and a significant association between concentration of microbial indicators in hand rinse samples and concentration in produce rinse samples (β=0.17-0.57, 95% CI=0.03-0.69). Consistent with prior studies, farms in this study employed techniques that carry a lower risk of microbial contamination including the irrigation of produce with well water from irrigation drip-tape hoses and the use of synthetic fertilizer covered by plastic mulch. Mechanistically, the relationship between hand and produce contamination may be explained by effective microbial adherence and transfer as well as repeated contact between hands and produce. These results highlight the need for interventions surrounding farmworker hygiene and sanitation to interrupt microbial adherence and persistence on farmworkers hands.

Table of Contents

Chapter 1: Comprehensive Review of the Literature ...1
Burden of Produce-Related Foodborne Illnesses... 1
Common Foodborne Pathogens Associated With Produce ...3
Fecal Indicators as a Proxy for Foodborne Pathogen Contamination... 4
Sources of Produce Contamination on Farms ...6
Detection Methods ...11
Goal ...12
Significance ...13
Chapter 2: Manuscript.. 14
Introduction... 14
Methods... 17
Study area ...17
Sample collection... 17
Produce rinses ...18
Water ...19
Soil ..19
Hand rinses ...20
Microbial indicator testing ...20
Statistical Analyses... 22
Results... 24
Discussion ...28
Strengths and Limitations... 35
Tables and Figures... 36
Chapter 3: Conclusion and Recommendations ...41
Conclusion... 41
Recommendations ...42
References ..44
Appendices ...52

About this Master's Thesis

Rights statement
  • Permission granted by the author to include this thesis or dissertation in this repository. All rights reserved by the author. Please contact the author for information regarding the reproduction and use of this thesis or dissertation.
  • English
Research field
Committee Chair / Thesis Advisor
Committee Members
Partnering Agencies
Last modified

Primary PDF

Supplemental Files