Irritable bowel syndrome: the role of the intestinal microbiota, pathogenesis and therapeutic targets.

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder that predominantly affects women and accounts for up to 40% of the gastroenterology unit outpatient visits. The pathophysiology is complex and multifactorial. In the present review we will focus on the role of intestinal dysbiosis in its pathogenesis and treatment. Post-infectious IBS (PI-IBS) can put light on the mechanisms underlying IBS. Modified commensal gut flora may lead to mucosal inflammation. Several changes such as an increase in mucosal cellularity (enterochromaffin cells, lamina propria T lymphocytes and mast cells), modified pro-inflammatory/anti-inflammatory cytokine balance and disordered neurotransmission have been observed. The normal microbiota is an essential factor in health. A modification of the flora, such as small intestinal bacterial overgrowth (SIBO) is thought to play a pathogenic role in IBS. Changes in the composition of the luminal and mucosal colonic flora have been linked to IBS. It is not clear however, whether these changes are a cause or a consequence of the syndrome. The comprehension of the interaction between the dysbiotic microbiota and the host will probably lead to the development of focused therapies. Based on these assumptions, treatments modulating the microbiota have been investigated. On the one hand several probiotics have shown a reduction in IBS symptoms by an immunomodulatory and analgesic effects. On the other hand antibiotic treatment has proven efficacy in treating IBS with or without associated SIBO. Due to its complex pathophysiology, treating IBS nowadays implies multiple approaches, one of which may be modulation of the intestinal flora.