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Title: Studies on the influence of essential oils on human gut bacteria and colonic cells
Author: Thapa, Dinesh
ISNI:       0000 0004 5366 6551
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 2015
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The ability of essential oils (EO) to manipulate the intestinal microbiota may potentiate their application in food as nutraceutical and as prophylactic agents for colonic disease. Little is known about the influence of EO on gut bacteria, the mechanism of their antibacterial action and genotoxicity to the host. Here, the antibacterial activities of EO in pure and in a mixed faecal culture were investigated. These antibacterial activities were further studied to compare the selective nature of EO and their effects on membrane integrity. The growth of gut pathogens and commensals was inhibited in a dose-dependent manner in pure culture, with most of the pathogens, Escherichia coli O157:H7, Clostridium difficile, C. perfringens and Salmonella typhimurium are sensitive to nerolidol, thymol, eugenol and geraniol at a half maximal inhibitory concentration (IC50) of 50-500 ppm. These concentrations of EO and mainly nerolidol were also inhibitory to some gut commensals, in particular affecting Faecalibacterium prausnitzii adversely in pure culture. In contrast, in the mixed culture system beneficial groups of bacteria, including F. prausnitzii, as determined by qPCR of 16S rRNA genes were not affected. Thymol and geraniol at 500 ppm suppressed the growth of total bacteria, resulting in minimal fermentation. A lower dose of 100 ppm of EO compounds was effective in suppressing the pathogen, C. difficile with no concern for commensal bacteria or their fermentation products, acetate, propionate and butyrate. This study also discovered that the proteome of commensal, Faecalibacterium prausnitzii and pathogenic gut bacteria, Escherichia coli, in response to EO compounds are affected differently. Thymol and eugenol down-regulated virulence factors in E. coli. The tested EO compounds were not genotoxic in the comet assay at non-toxic doses. Differential effects of EO compounds on gut pathogens and commensals and their non-toxicity but geno-protective properties could be applicable in improving gut health in man.
Supervisor: Not available Sponsor: Scottish Overseas Research Student Awards ; College of Life Sciences and Medicine ; University of Aberdeen ; Agolin SA ; Bière ; Switzerland
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Essences and essential oils ; Gastrointestinal system ; Colon (Anatomy)