Purpose of review To review recently published studies investigating any association between gut flora and symptoms of irritable bowel syndrome.

Recent findings Experimental studies demonstrate associations between gut flora, gut motility, mucosal inflammation and visceral hypersensitivity. Scientific bases for possible benefits of selected probiotics on irritable bowel symptoms have been identified. Disturbances in viable counts of fecal flora have been demonstrated in patients with irritable bowel syndrome. Results of studies based on breath tests are conflicting as to whether the prevalence of small intestinal bacterial overgrowth is increased in this group. Nonetheless, a longitudinal analysis based on bacteriological assessments of serial small intestinal aspirates suggests that this entity should be considered in patients with irritable bowel symptoms, especially in the setting of predisposition to bacterial overgrowth. Clinical trials of probiotic treatment for irritable bowel syndrome have yielded conflicting results.

Summary Recent studies provide increasing support for the concept that disturbances in gut flora occur in patients with irritable bowel syndrome and that such abnormalities may contribute to irritable bowel syndrome-type symptoms. The relative importance of disturbed gut flora to symptom pathogenesis, along with the therapeutic potential of modulation of the gut flora for amelioration of irritable bowel syndrome symptoms, however, remains to be fully defined.