Campylobacter rectus Bacterial-Host Interactions in Pathogenesis
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Campylobacter rectus is a Gram-negative oral anaerobe and a causative agent of periodontitis. Additionally, C. rectus strains have been isolated from patients with oral and extraoral abscesses, gingival crevices, and appendicitis. This organism has been implicated in bacteremia and is associated with pre-term births and low birth weight, indicating its importance as an emerging pathogen. The goal of this thesis was to establish genetic tools to begin clarifying mechanisms responsible for C. rectus pathogenesis. In particular, secretion systems identified as important for pathogenesis in related bacterial species were selected for further study. Bacterial-host interaction assays were used to identify host responses stimulated by the CiaB protein as well as the role of the Hcp protein in host cell adherence. Toward this goal, complete deletions of the ciaB and the hcp genes were generated in C. rectus and reference genes for RT-qPCR in C. rectus were validated to permit assessment and verification of the mutant strains. Host response was assessed by exposing a human placental epithelial cell line, BeWo, to both C. rectus wild-type and ciaB mutant strains for six-hours under anaerobic conditions and inflammatory mRNA expression was measured using RT-qPCR. A significant upregulation in 41 inflammatory genes was measured in response to ΔciaB while only three were significantly upregulated in response to wild-type. THP-1 human monocyte cell viability was also assessed over a 96-hour time course after exposure to wild-type and ΔciaB. Additionally, adherence efficiencies of wild-type and Δhcp to BeWo cells were calculated after a one-hour time point. Adherence rates between wild-type and Δhcp were not significantly different. The studies in this thesis suggest C. rectus uses CiaB as a mechanism to evade the host cell immune response. Analysis of the Δhcp mutant prepared this strain for further studies like those used for the CiaB mutant strain to fully characterize the importance of the type VI secretion system to C. rectus virulence. Results from this foundational thesis research will expedite future studies examining the underlying molecular mechanisms of C. rectus pathogenesis.
Kinder, Meghan Nichole (2017). Campylobacter rectus Bacterial-Host Interactions in Pathogenesis. Master's thesis, Texas A & M University. Available electronically from