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Examining the Effects of Defined Microbial Ecosystems on Clostridioides difficile Growth and Virulence

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Title: Examining the Effects of Defined Microbial Ecosystems on Clostridioides difficile Growth and Virulence
Author: Carlucci, Christian
Department: Department of Molecular and Cellular Biology
Program: Molecular and Cellular Biology
Advisor: Allen-Vercoe, Emma
Abstract: Many cases of Clostridioides (formerly, Clostridium) difficile infection (CDI) are unresponsive to current antibiotic treatment strategies, and often patients suffer from recurrent infections characterized by severe diarrhea and colonic inflammation. We have developed a defined and standardized stool-derived microbial ecosystem therapeutic (MET-1), which was used to cure two patients of recurrent CDI (rCDI) in a proof-of-principle trial. To investigate the mechanisms behind the ability of the healthy human gut microbiota to protect against C. difficile in vitro, we used MET-1 and other defined microbial ecosystems to model health and disease states. Using a single-stage chemostat distal gut model to support the growth of bacterial communities, we characterized the compositional and metabonomic profiles of two defined microbial ecosystems derived from the microbiota of a healthy donor (MET-1 and DEC58), and two ecosystems representative of a dysbiotic state. Dysbiotic ecosystems were individually created through both the omission of Lachnospiraceae from DEC58, and treatment of chemostat-cultured DEC58 with ciprofloxacin, a broad-spectrum fluoroquinolone antibiotic. Both perturbed ecosystems were shown to have altered, but distinct taxonomic and metabonomic compositions compared to DEC58. We then examined the effects of defined microbial ecosystem-associated metabolites on the vegetative cell growth, sporulation, germination, spore outgrowth, toxin gene expression and secretion of two clinically important C. difficile ribotype strains, 027 and 078. Additionally, the cytotoxicity and metabonomic profiles of C. difficile were assessed in response to treatment with each defined microbial ecosystem. Although there was large heterogeneity in the growth and virulence determinants of C. difficile strains in response to defined microbial ecosystems, the results from this study suggest that defined microbial ecosystem-associated metabolites may influence C. difficile virulence by decreasing secreted TcdA and TcdB levels in vitro and protecting against TcdB-mediated cytotoxicity. The identification of these antagonistic properties complements our existing knowledge of gut microbiota-specific anti-virulence mechanisms against C. difficile, and will guide the development and optimization of novel defined microbial ecosystem formulations for the effective treatment of rCDI.
Date: 2017-03
Rights: Attribution-NoDerivs 2.5 Canada
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Attribution-NoDerivs 2.5 Canada Except where otherwise noted, this item's license is described as Attribution-NoDerivs 2.5 Canada