Host Pathogen responses of chicken cells in vitro and in vivo to a diverse population of Campylobacter strains

Abstract

Campylobacter is the leading cause of bacterial food-borne diarrheal disease worldwide, with the bacteria being pathogens in humans and chickens. There are differences in the mechanistic understanding between Campylobacter strains, due, in part, to genomic and phenotypic strain diversity, which leads to inconsistent findings. This study aimed to understand underlying infection biology in host-pathogen interactions between populations of Campylobacter and the chicken host. A collection of Campylobacter jejuni strains were used to investigate the genotypic and phenotypic differences which yielded a diverse pan-geome of 2715 genes with genome wide association studies uncovering genes related to flagella assocaited with strains isolated from both humans and chickens. The C. jejuni strains were then used with a new commercially available chicken cell line to investigate the chicken systems with host responses measured in comparison to human systems. The pathogenic diversity of C. jejuni was measured through their inflammatory, cytotoxicity, adhesion, invasion and signalling responses in a high-throughput model using avian and human intestinal epithelial cells. C. jejuni induced IL-8 and CXCLi1/2 in human and avian epithelial cells, respectively, in a MAP kinase-dependent manner. In contrast, IL-10 responses in both cell types were PI 3kinase/Akt-dependent. C. jejuni strains showed diverse levels of invasion with high invasion dependent on MAP kinase signaling in both cell lines. C. jejuni induced diverse cytotoxic responses in both cell lines with cdt-positive isolates showing significantly higher toxicity. Blockade of endocytic pathways suggested that invasion by C. jejuni was clathrin-and dynamin-dependent but caveolae-independent in both cells. In contrast, IL-8 (and CXCLi1/2) production was dependent on clathrin, dynamin, and caveolae. Strong correlations were found between IL-8 with invasion and toxicity responses with GWAS being able to associated genes to expression of IL-8,-10 and level of invasion. Campylobacter strains were isolated from the caeca, ileum and liver and a pan-genome created with GWAS analysis discovering genes relating to iron transport and heat shock proteins in strains from the liver. Subsequently, caecal tonsils were extracted from chickens uninfected and chickens infected with a cocktail of six Campylobacter strains with a Campylobacter effect found where infected chickens produced significantly higher T h 1, T h 2 and T h 17 cytokines. The work in this thesis contributes invaluable knowledge on the chicken innate immune system in response to Campylobacter and how similar host defence pathways to humans are utlised. The diversity found strongly indicates that a "one strain fits all" approach to in vitro and in vivo experimental infections may not give accurate results on Campylobacter pathogenesis. Campylobacter isolates can use host immune responses to its advantage and to move from the gut of chickens to infect edible tissues such as the liver.