Date of Graduation

12-2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Cell & Molecular Biology (PhD)

Degree Level

Graduate

Department

Biological Sciences

Advisor/Mentor

Xiaolun Sun

Committee Member

Billy M. Hargis

Second Committee Member

Young M. Kwon

Third Committee Member

Yuchun Du

Keywords

Bacterial pathogen, Bile acids, Campylobacter jejuni, Clostridium perfringens, Microbial metabolites, Microbiota

Abstract

Campylobacter jejuni (C. jejuni) and Clostridium perfringens (C. perfringens) are two leading pathogenic bacteria responsible for both human and animal diseases. In chapters Ⅱ to Ⅳ, I presented an overview of current knowledge on the role of immune response, microbiota, bile acids and their microbial metabolites on campylobacteriosis, and C. perfringens induced necrotic diseases.In chapter Ⅴ, I investigated effects of deoxycholic acid-modulated anaerobes (DCA-Anaero) on attenuating chicken transmission-exacerbated campylobacteriosis. SPF Il10-/- mice were gavaged with clindamycin for 7 days followed by infected with three C. jejuni strains, Cj-P0 (C. jejuni AR101), Cj-P1 (from chicken pre-infected with C. jejuni AR101), and Cj-P1-DCA-Anaero (from C. jejuni AR101 infected chicken pre-colonized with DCA-Anaero) at day 0 and euthanized at day 8. As a result, Cj-P1 induced more severe histopathology compared to Cj-P0, suggesting that chicken transmission increased C. jejuni virulence. Importantly, mice infected with Cj-P1-DCA-Anaero showed attenuation of intestinal inflammation compared to Cj-P1, which suggest that DCA-Anaero attenuate chicken-transmitted campylobacteriosis in mice and it is important to control the elevation of C. jejuni virulence during chicken transmission process. In our previous research, we also found that DCA could control chicken necrotic enteritis (NE) by reducing C. perfringens invasion and sporulation. In chapter Ⅵ, I developed vaccines using C. perfringens sporulation proteins (CP-spor-super1&2) and examined their effects on reducing NE in chickens. Broiler chickens were vaccinated at day 0, and had a booster vaccination at day 10, followed by infected with Eimeria maxima at day 16, and C. perfringens at day 20. Chickens were euthanized, and samples were collected at day 21. Vaccinated birds were resistant to severe clinical NE on histopathology and body weight gain loss. CP-spor-super1 vaccine reduced NE-induced proinflammatory Ifnγ gene expression as well as C. perfringens luminal colonization and tissue invasion in the small intestine (SI). Together, this study showed that CP-spor-super vaccines reduced NE manifestations such as histopathology and productivity loss. Inspired by the colonization susceptibility of C. jejuni on different conventional animals with various gut bile acids compositions, in chapter Ⅶ, I investigated the role of specific bile acid microbial metabolites on C. jejuni infection. Chickens gavaged with CA developed mild resistance to C. jejuni colonization and had increased CA levels in SI. C. jejuni-resistant conventional Il10-/- mice became highly susceptible to campylobacteriosis when fed CDCA diet, while no pathogen and colitis were found in basal diet group. Mechanism studies showed that mouse microbiota or bile acid alone reduced C. jejuni in vitro growth moderately, while CDCA microbial metabolites promoted C. jejuni in vitro growth, and CA microbial metabolites inhibited C. jejuni in vitro growth. The results suggest animal susceptibility to C. jejuni is mediated by microbiota-metabolized host-specific bile acids. Taken together, this dissertation showed that DCA-Anaero attenuated C. jejuni chicken transmission-worsened enteritis in clindamycin treated mice; vaccines using C. perfringens sporulation proteins reduced NE in chickens; host-specific CDCA and CA microbial metabolites differentially mediated C. jejuni infectiousness. All of these findings showed that specific bile acid microbial metabolites played important roles in C. jejuni or C. perfringens infection.

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Available for download on Monday, February 17, 2025

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