Date of Completion

11-1-2016

Embargo Period

10-31-2017

Keywords

Clostridium difficile, meat, Carvacrol, Trans-cinnamaldehyde, mouse model

Major Advisor

Dr. Kumar Venkitanarayanan

Associate Advisor

Dr. Mary Anne Roshni Amalaradjou

Associate Advisor

Dr. Cameron Faustman

Associate Advisor

Dr. Bhushan M. Jayarao

Associate Advisor

Dr. Joan A. Smyth

Field of Study

Animal Science

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

Clostridium difficile is a significant pathogen causing a toxin-mediated enteric disease in humans and animals. The incidence and severity of C. difficile associated disease (CDAD) in humans have increased in the US with the emergence of hypervirulent strains and community associated outbreaks. The detection of genotypically similar and identical C. difficile strains implicated from human infections in foods and food animals suggest the potential role of food as a source of community-associated C. difficile disease. C. difficile predominantly affects hospital inpatients undergoing prolonged antibiotic therapy, which results in enteric dysbiosis, leading to C. difficile spore germination, pathogen colonization in the intestine and subsequent toxin production. Therapeutic agents that inhibit critical C. difficile virulence factors such as toxin production, sporulation, and spore outgrowth without causing enteric dysbiosis could improve the clinical outcome of C. difficile infections and prevent relapse of the infection. In this Ph. D. research work, the efficacy of two plant-derived molecules, carvacrol (CR) and trans-cinnamaldehyde (TC), were investigated for reducing C. difficile toxin production. Gene expression and cell culture studies were performed to elucidate the mechanisms behind the anti-toxigenic mechanism of CR and TC. Moreover, the efficacy of CR on C. difficile sporulation, germination, and spore outgrowth was also investigated. Furthermore, the effect of CR on CDAD pathogenesis was investigated in a mouse model with special reference to its effect on themouse gut microbiome. The results revealed that sub-inhibitory concentrations (SIC) of CR and TC reduced CD toxin production and cytotoxicity in vitro by downregulating toxin production genes (pC. difficile sporulation and spore outgrowth. Oral supplementation of CR improved the clinical outcome in the C. difficile challenged mice, and positively altered the gut microbiome composition (pC. difficile was investigated, where beef, pork and chicken samples obtained from geographically distant grocery stores in Connecticut were tested for C. difficile. Presumptive C. difficile isolates were characterized by ribotyping, antibiotic susceptibility, toxin production and whole genome sequencing. The results revealed that C. difficile occurs at very low levels in raw meat sold in Connecticut, but the isolates were resistant to multiple antibiotics.

Available for download on Tuesday, October 31, 2017

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