Reinvestigation into the mechanisms of Campylobacter jejuni invasion of intestinal epithelial cells

Background: Campylobacter jejuni is an important foodborne pathogen and the leading cause of bacterial gastroenteritis. Despite the importance of C. jejuni infection and decades of research, the mechanisms for colonisation of the human intestinal tract by C. jejuni and how this causes diarrhoeal disease remain unclear, with a significant number of conflicting reports in the literature creating controversy in this area. Methods: The effect of different inhibitors of host cell pathways on the ability of the C. jejuni 81-176 wild-type strain to interact with and invade intestinal epithelial cells (IECs) was investigated. Defined isogenic C. jejuni 81-176 & 11168H ciaB, cadF and flpA mutants were constructed and characterised for the ability to interact with and invade host cells. Results: Disruption of microfilaments with Cytochalasin D increased C. jejuni invasion. Disruption of caveolae-mediated endocytosis with Methyl-beta-cyclodextrin, disruption of microtubules with Colchicine, disruption of clathrin-mediated endocytosis with Monodansylcadaverine, inhibition of phosphatidylinositol 3-kinase with Wortmannin all decreased C. jejuni invasion. Infection of the Galleria mellonella insect model with ciaB, cadF and flpA mutants resulted in a significantly reduced cytotoxic effect on the larvae. The ability of ciaB, cadF and flpA mutants to interact with and invade Caco-2 and T84 IECs was significantly reduced. The ciaB, cadF and flpA mutants exhibited a more significant decrease in the number of invasive bacteria when co-cultured with IECs in the Vertical Diffusion Chamber model. Pre-treatment of Caco-2 IECs with OMVs isolated from the ciaB, cadF and flpA mutants reduced interactions and invasion of these IECs by live C. jejuni. Conclusion: C. jejuni invasion of IECs involves modulation of many host cell pathways. CiaB, CadF and FlpA all play an important role in C. jejuni interactions with IECs leading to bacterial invasion. Further studies are still required to elucidate the exact roles that these important C. jejuni virulence factors play during interactions with and invasion of host cells.