Microbiota and the irritable bowel syndrome

Gut microbiota plays a vital role in human health. The number of microorganisms inhabiting the gastrointestinal (GI) tract has been estimated to exceed 1013. The dominant genera in the human intestine are Firmicutes (more than 180 species of Lactobacillus), Actinobacteria (among others the Bifidobacteriae), Bacteroidetes (the most important is B. fragilis) and Proteobacteria (E. coli, Salmonella, Yersinia, Shigella, Vibrio, Haemophilus, etc.), but the composition of the flora varies individually, as well as in relation to factors such as host genetics, stress, diet, antibiotics and early childhood experiences. Irritable bowel syndrome (IBS) is one of the most common functional gastrointestinal disorders (FGIDs), which has now been renamed disorders of gut-brain interaction, which affect a large number of people worldwide. It is characterized by abdominal pain and altered bowel habits in the absence of obvious anatomic or physiologic abnormalities. It poses a negative economic impact to the global health care system in addition to reducing the quality of life in patients. The pathophysiology of IBS is not fully understood. In IBS subjects gut microbiota relative to healthy controls was observed with an increase in Enterobacteriaceae, Ruminococcus, Clostridium, Dorea species and a decrease of Lactobacillus, Bifidobacterium, and Faecalibacterium species. IBS with diarrhea predominance (IBS-D) IBS with mixed bowel habits (IBS-M) share similarities in the microbial profile. Recent studies suggest that perturbations within "brain-gut-microbiota" axis may lead to IBS development. The aim of this review was to highlight the potential role of gut microbiota on pathophysiological mechanisms underlying IBS.