Date of Completion

7-28-2017

Embargo Period

7-27-2020

Keywords

E. coli O157: H7, selenium, rutin

Major Advisor

Dr. Kumar Venkitanarayanan

Associate Advisor

Dr. Cameron Faustman

Associate Advisor

Dr. Mary Anne Roshni Amalaradjou

Associate Advisor

Dr. Paulo Verardi

Field of Study

Animal Science

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

Enterohemorrhagic E.coli O157: H7 (EHEC) has emerged as one of the leading causes of food borne illness and pediatric diarrheal disease in the United States. The EHEC associated life-threatening hemolytic uremic syndrome in human patients is linked to the expression of several virulence factors of the pathogen, especially verotoxins. Verotoxins (VT) or shiga like toxins (Stx) are the major virulence factors elaborated by EHEC. Even after 30 years of research on EHEC epidemiology and pathogenesis, little advancement has been made in disease prevention and treatment against the bacterium. One of the main limitations in treating EHEC infection is the contraindicated usage of antibiotics since they have been reported to exacerbate verotoxin-mediated HUS and renal failure. Therefore, there is a crucial need for the development of alternate interventions for preventing and treating EHEC infections in humans. EHEC being a foodborne pathogen, controlling its persistence in meat processing facilities and inactivating the pathogen in high-risk foods such as undercooked ground beef products could potentially reduce food-borne disease outbreaks in humans. Moreover, identifying drugs that attenuate EHEC virulence, especially verotoxins would reduce the severity of infection and improve disease outcome in humans. This dissertation investigated the potential of a phytochemical, rutin (RT), and an essential mineral, selenium (Se), for targeting EHEC from both these aspects, thereby reducing risks to humans. Specifically, the efficacy of Se in reducing EHEC biofilms on food contact surfaces, and the efficacy of RT for decreasing EHEC in undercooked ground beef were investigated. Selenium was found to be effective in inhibiting and inactivating EHEC on abiotic surfaces. In addition, coating of stainless steel surface with Se nanoparticles exerted significant antibiofilm effect against EHEC (P < 0.05). On the other hand, RT significantly increased heat inactivation of EHEC in undercooked ground beef patties without adversely affecting meat color and shelf-life. In addition, mechanistic investigations on the anti-virulence property of these natural antimicrobials revealed that Se and RT significantly decreased both intracellular and extracellular verotoxin synthesis (P < 0.05). In addition, Se decreased EHEC toxin receptor expression in host cells, whereas RT competed for the receptor binding sites on the toxin. Moreover, RT decreased EHEC motility and adhesion to cultured intestinal epithelial cells (P< 0.05). Subsequently, the protective effect of RT and Se against EHEC was validated in vivo using Caenorhabditis elegans model. Rutin significantly increased the survival of EHEC-infected C. elegans compared to control worms, where the survivability was increased by ~ 65% (P < 0.05). However, Se was lethal to C. elegans, and at very low sub-lethal dose failed to protect the worms when challenged with EHEC.

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