Characterizing relationships between bacterial indicators of foodborne pathogens on Mexican produce in the pre-harvest and post-harvest environment Público
Usher, Rachel (Spring 2020)
Abstract
In recent decades, the United States has experienced a rise in the number of foodborne disease outbreaks impacting millions of Americans every year. The majority of these new outbreaks originate from contaminated produce. Testing for foodborne pathogens such as pathogenic E. coli and Salmonella in agricultural samples is expensive and time consuming, so indicator bacteria of fecal contamination are commonly used to detect poor sanitation on agricultural products.
There are many potential sources of produce contamination in the agricultural environment including irrigation water, soil, farming equipment, and farmworker hands. Currently, there is little understanding of the fitness and relationships between indicator bacteria and pathogenic enteric bacteria on these surfaces and substrates in the agricultural environment. This study aims to characterize the relations between different bacterial indicators to see if these relationships are modified by sample type at different processing stages from Mexican farms distributing different types of produce.
Between 2011 and 2012, samples were collected from 11 farms producing three types of produce (cantaloupe, tomato, jalapeños), on different associated sample types (produce, soil, irrigation water, hand-rinse), before and after harvest. Each sample was analyzed for the presence and concentration of three bacterial indicators: E. coli, coliforms, and Enterococcus. In an analysis of the principal component 1 scores we found significant differences in the mean score values between produce samples in the pre-harvest (p < 0.005) and post-harvest (p < 0.001) environment in addition to significant differences between hand-rinse scores (p < 0.05). In all of these comparisons, the cantaloupe associated scores were significantly larger than tomato and jalapeño. We also found significant differences in the indicator bacteria relationships in the discriminant analysis among cantaloupe samples compared to the other produce types. Overall, relationships between bacterial indicators vary significantly by associated sample and produce type indicating physical characteristics of produce, such as the rough skin of a cantaloupe, may create a more ideal habitat for colonization by indicator bacteria than the waxy produce surfaces of jalapeño and tomato. This study will contribute much needed initial research characterizing the relative abundance and association of indicator bacteria within the agricultural environment.
Table of Contents
Literature Review 8
Data and Methods 20
Study Sites 20
Study Design 21
Statistical Analyses 22
Results 24
Descriptive Statistics 24
Examining the quantity and concentration of indicators 24
Assessing relationships between indicators 25
Contribution of bacterial indicators to the contamination profile 30
Contamination modified by sample type and associated produce type 31
Relationship between bacterial indicators 33
Strengths and limitations 35
Implications 37
References 38
Figures and Tables 48
Table 1. Summary statistics 48
Table 2. Principal component results 49
Figure 1. Significantly different produce and hand-rinse cantaloupe PC1 scores 50
Figure 2. Discriminant analysis plots by produce type and time period 52
Table 3. Discriminant analysis score summaries 54
Appendix A: IRB Approval 56
About this Master's Thesis
| School | |
|---|---|
| Department | |
| Subfield / Discipline | |
| Degree | |
| Submission | |
| Language |
|
| Research Field | |
| Palabra Clave | |
| Committee Chair / Thesis Advisor |
Primary PDF
| Thumbnail | Title | Date Uploaded | Actions |
|---|---|---|---|
|
|
Characterizing relationships between bacterial indicators of foodborne pathogens on Mexican produce in the pre-harvest and post-harvest environment () | 2020-04-27 17:50:35 -0400 |
|
Supplemental Files
| Thumbnail | Title | Date Uploaded | Actions |
|---|