An irritable bowel syndrome subtype defined by species-specific alterations in faecal microbiota

Background and aims Irritable bowel syndrome (IBS) isa common functional gastrointestinal disorder that maybe triggered by enteric pathogens and has also beenlinked to alterations in the microbiota and the hostimmune response. The authors performed a detailedanalysis of the faecal microbiota in IBS and controlsubjects and correlated the findings with key clinical andphysiological parameters.Design The authors used pyrosequencing to determinefaecal microbiota composition in 37 IBS patients (meanage 37 years; 26 female subjects; 15 diarrhoeapredominantIBS, 10 constipation-predominant IBS and12 alternating-type IBS) and 20 age- and gendermatchedcontrols. Gastrointestinal and psychologicalsymptom severity and quality of life were evaluated withvalidated questionnaires and colonic transit time andrectal sensitivity were measured.Results Associations detected between microbiotacomposition and clinical or physiological phenotypesincluded microbial signatures associated with colonictransit and levels of clinically significant depression in thedisease. Clustering by microbiota composition revealedsubgroups of IBS patients, one of which (n=15) showednormal-like microbiota composition compared withhealthy controls. The other IBS samples (n=22) weredefined by large microbiota-wide changes characterisedby an increase of Firmicutes-associated taxa anda depletion of Bacteroidetes-related taxa.Conclusions Detailed microbiota analysis of a wellcharacterisedcohort of IBS patients identified severalclear associations with clinical data and a distinct subsetof IBS patients with alterations in their microbiota thatdid not correspond to IBS subtypes, as defined by theRome II criteria.