Doctoral Dissertations

Date of Award

5-2023

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Microbiology

Major Professor

Jeremiah G. Johnson

Committee Members

Elizabeth Fozo, Tim Sparer, Heidi Goodrich-Blair, Gina Pighetti

Abstract

Campylobacteriosis, the foodborne disease caused by Campylobacter spp., infects one out of 10 individuals every year. C. jejuni accounts for 90% of these infections resulting in numerous postinfectious disorders including the development of colorectal cancer, Guillain-Barré syndrome, irritable bowel syndrome, and reactive arthritis. Despite its large impact on human health, the host immune response to the bacterium is largely uncharacterized. Chapter two of this dissertation addresses the development of neutrophil extracellular traps (NETs) within human and ferret campylobacteriosis. We observed NET-associated proteins increase in the feces of C. jejuni-infected patients and that in vitro C. jejuni induces NETs, which are cytotoxic to colonic epithelial cells. Furthermore, we observed NET-like structures within intestinal tissue of C. jejuni-infected ferrets where C. jejuni colonizes and causes tissue pathology. The work presented in chapter three of this dissertation characterizes a novel secreted C. jejuni effector, a sirtuin-like protein (SliP), which we found induces NETs. SliP is secreted into neutrophils, where it deacetylates proteins, specifically histone H3. As histone H3 acetylation plays a crucial role in chromatin structure and host transcription, activity of SliP could have immense impacts on the host cell physiology. Leveraging the murine model of campylobacteriosis, we determined a C. jejuni sliP mutant efficiently infects mice, but induction of proinflammatory cytokines and gastrointestinal pathology is decreased compared to wild-type C. jejuni infected mice demonstrating the importance of this protein in immune pathology in vivo. Finally, the work done in chapter four of this dissertation sought to characterize a C. jejuni nuclease (MugA) and its ability to assist in NET evasion. In this work, we performed a transposon screen of C. jejuni for nuclease production. We discovered that a mugA mutant was sensitive to NET killing and lacked nuclease activity. Interestingly, MugA degraded NETs lead to inflammasome activation within macrophages, and subsequent host inflammation. In conclusion, this dissertation demonstrates the influence of NETs within campylobacteriosis and highlights a potential target for therapeutic strategies. By specifically targeting SliP and MugA in C. jejuni for their role in immune modulation, these could be attractive therapeutics to reduce host inflammation and potential post-infectious disorder onset.

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