Theses and Dissertations

Issuing Body

Mississippi State University

Advisor

Smith, David R.

Committee Member

Bailey, R. Hartford

Committee Member

Erickson, Galen E.

Committee Member

Huston, Carla L.

Committee Member

Wills, Robert W.

Date of Degree

12-8-2017

Original embargo terms

Worldwide

Document Type

Dissertation - Open Access

Major

Veterinary Medical Research

Degree Name

Doctor of Philosophy

College

College of Veterinary Medicine

Department

Veterinary Medical Science Program

Abstract

Enterohemorrhagic Escherichia coli (EHEC) are important foodborne pathogens with a bovine reservoir. For many years, research and regulations have focused on the EHEC serogroup most commonly associated with severe human illness, EHEC O157. However, six additional EHEC serogroups have been identified as important human foodborne pathogens and have been declared adulterants in raw, non-intact ground beef by the United States Department of Agriculture’s Food Safety Inspection Service. Collectively these seven organisms are referred to as EHEC-7. With the addition of these six pathogens, epidemiological studies are needed to estimate the probability for cattle to carry them and to identify risk factors associated with their presence in samples of bovine origin. In addition, the potential for pre-harvest control of EHEC-7 in feedlot cattle, particularly by dietary intervention, is a knowledge gap that needs to be addressed. Finally, detection methods of EHEC-7 have not been validated, and there is no “gold-standard” test. The first study included in this dissertation was a cross-sectional study estimating the prevalence and risk factors associated with hide contamination by EHEC-7 on the hides of market beef cows at slaughter. The second study was a longitudinal analysis of EHEC-7 from fecal samples from cow-calf herds in Mississippi and Nebraska. The third study was a randomized controlled trial evaluating the effects of fiber from distillers grains on the probability to detect EHEC-7 in samples from the rectoanal mucosa of feedlot steers. The fourth study included in this dissertation was a Bayesian latent class analysis estimating the diagnostic performance of three EHEC-7 detection methods, specifically modeling the performance and prevalence of EHEC O157 in fecal samples from beef cow-calf herds.

URI

https://hdl.handle.net/11668/19541

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