Abnormal expansion of segmented filamentous bacteria in the gut: a role in pathogenesis of chronic inflammatory intestinal diseases?

Human intestinal microbiota create a complex polymicrobial ecology characterized by high population density, wide diversity, and complexity of interactions. Any imbalance of this complex intestinal microbiome, both qualitative and quantitative, might have serious health consequences including an increase in the number and/or alteration in the type of bacteria in the upper gastrointestinal tract, which is referred to as small intestinal bacterial overgrowth (SIBO) syndrome. SIBO is frequently found in persons fulfilling criteria for irritable bowel syndrome (IBS), and the large overlapping of symptoms of these two pathological conditions led some authors to believe that IBS is secondary to SIBO. Interestingly, SIBO is also found in about 25% of patients with Crohn's disease. Emerging data show that specific components of gut microbiota, particularly segmented filamentous bacteria (SFB), activate intestinal immunocompetent cells, for example, Th17 cells which have a potential role in pathogenesis of inflammatory intestinal diseases. On the basis of the aforementioned data we postulate that a previously unidentified specific form of SIBO, involving in particular the aberrant expansion of SFB in the gut, could play a role in the onset of chronic intestinal inflammatory diseases through persistent activation of Th17 cells. From this point of view, a successful therapeutic approach to inflammatory intestinal disease patients could be the administration of specific antibiotics directed against SFB to restore the physiological levels of these bacteria in the gut. Furthermore, it could be very useful to identify appropriate laboratory methodologies to monitor the level of SFB in the gut with the aim of preventing their potentially dangerous increase in numbers. (C) 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins