Probiotics in irritable bowel syndrome: Where are we?

We have only recently begun to understand how alterations of the intestinal microbial ecosystem lead to the disruption of host-microbial interactions and are associated with diseases, including functional gastrointestinal disorders such as irritable bowel syndrome (IBS). Although we are still far from understanding the human microbiome, gut microbiota is already a therapeutic target. Probiotics are live microorganisms that, when administered in adequate amounts, confer a health benefit to the host and may represent a therapeutic option for diseases characterized by dysbiosis such as IBS. Meta-analyses suggest that probiotics provide a therapeutic gain over placebo on global symptoms with a high safety profile in IBS patients. However, the mechanisms by which they provide benefit in IBS remain virtually unknown. In this issue of Neurogastroenterology and Motility, BIO-25, a multispecies probiotic, did not significantly modify the composition of the fecal microbiota, but interestingly, patients with specific basal features of the intestinal microbial ecosystem improved with treatment. Based on these data, it is tantalizing to speculate that microbiota composition serves as a predictor of the response to probiotic intervention. This mini-review addresses unresolved issues related to mechanisms through which probiotics may exert their beneficial effects, the biological, as well as clinical predictors of favorable outcomes in IBS and finally considers possible new directions for future studies.