Elucidation of enteric virulence of Campylobacter concisus

Abstract

Campylobacter concisus is a Gram-negative mobile oral bacterium that has been shown to be associated with human inflammatory bowel disease. Various experiments were conducted in this PhD project, aiming to elucidate the enteric virulence of C. concisus. The growth of oral C. concisus strains under different atmospheric conditions was examined. It was found that 92 % of strains grew under anaerobic conditions without H2. However, none of the strains grew under microaerobic conditions without H2. The presence H2 greatly increased the growth of C. concisus under anaerobic conditions and enabled C. concisus to grow under microaerobic conditions. The H2 had no effects on the expression of a number of putative virulence factors in C. concisus. The effects of formate and fumarate, on the production of H2S in oral C. concisus were investigated. Supplementation of formate and fumarate significantly increased the positivity of H2S production. In addition, the fumarate significantly increased C. concisus growth. Bioinformatics analysis was conducted to search for potential virulence factors encoded by prophages. Four prophage elements were identified in the genome of C. concisus strain 13826 with putative attachment sites overlapping with tRNA. Each prophage elements contained a novel Xer phage integrase. It was found that CON_phi2 prophage encodes a Zot protein, and CON_phi3 encodes a Zot-like protein. Moreover, the phylogenetic analysis showed the horizontal gene transfer between Campylobacter species. Monoclonal antibody to C. concisus Zot was produced and verified. The impact of bile on the expression of Zot was examined. It was found that a full length and a cleaved fragment of Zot were released from C. concisus in the presence of ox bile. Whether C. concisus strains affect actin in the intestinal epithelial cell line, Caco2 cells, was examined. Some C. concisus strains significantly reduced the levels of β-actin and caused the redistribution of F-actin in Caco2 cells. These findings show that the enteric virulence of C. concisus is determined by bacterial, host and environmental factors.