Role of emerging Campylobacter species in inflammatory bowel diseases

The gut microbiota is a central player in the etiology of inflammatory bowel diseases. As such, there is intense scientific interest in elucidating the specific group/s of bacteria responsible for driving barrier damage and perpetuating the chronic inflammation that results in disease. Because of their ability to colonize close to the surface of the host intestinal epithelium, mucosa-associated bacteria are considered key players in the initiation and development of both Crohn's disease and ulcerative colitis. The leading bacterial candidates include adherent and invasive Escherichia coli, Helicobacter, Fusobacteria, Mycobacteria, and Campylobacter species. Of these, a member of the Campylobacter genus, Campylobacter concisus, has recently emerged as a putative player in the pathogenesis of inflammatory bowel diseases. Current research indicates that this bacterium possesses extraordinarily diverse pathogenic capacities as well as unique genetic and functional signatures that are defined by their ability to adhere to and invade host cells, secrete toxins, and the presence of a virulence-associated restriction-modification system. These characteristics enable the potential classification of C. concisus into distinct pathotypes, which we have named adherent and invasive C. concisus and adherent and toxinogenic C. concisus. In this review, we evaluate evidence for the role of emerging Campylobacter species in the pathogenesis of inflammatory bowel diseases.