Reaching out for the causative agent in inflammatory bowel disease: is there evidence for Chlamydia pneumoniae as a pathogenic factor?

In this issue of the Journal, Muller and colleagues attempt to define the role of specific bacterial pathogens, particularly Chlamydia pneumoniae, as causative agents in inflammatory bowel disease. Even if a major role for C. pneumoniae in the pathogenesis of inflammatory bowel disease could be ruled out, our current understanding of inflammatory pathways in Crohn's disease and ulcerative colitis implies that the search for other microorganisms as causative agents should continue.