Gut 61:997-1006 doi:10.1136/gutjnl-2011-301501
  • Irritable bowel syndrome
  • Original article

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

  1. Magnus Simrén3
  1. 1Department of Microbiology, University College Cork, Cork, Ireland
  2. 2Alimentary Pharmabiotic Centre, University College Cork, Cork, Ireland
  3. 3Department of Internal Medicine, Institute of Medicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden
  1. Correspondence to Dr Paul W O'Toole, Department of Microbiology, University College Cork, 447 Food Science Building, Cork, Ireland; pwotoole{at}
  1. Contributors IBJ: analysis and interpretation of data, drafting of the manuscript and statistical analysis. PWO'T: study concept and design, critical revision of the manuscript for important intellectual content and obtained funding. LÖ: acquisition of data. MJC: analysis and interpretation of data. JD: technical or material support. EMMQ: study concept and design and critical revision of the manuscript for important intellectual content. MS: study concept and design, critical revision of the manuscript for important intellectual content and obtained funding.

  • Accepted 22 October 2011
  • Published Online First 16 December 2011


Background and aims Irritable bowel syndrome (IBS) is a common functional gastrointestinal disorder that may be triggered by enteric pathogens and has also been linked to alterations in the microbiota and the host immune response. The authors performed a detailed analysis of the faecal microbiota in IBS and control subjects and correlated the findings with key clinical and physiological parameters.

Design The authors used pyrosequencing to determine faecal microbiota composition in 37 IBS patients (mean age 37 years; 26 female subjects; 15 diarrhoea-predominant IBS, 10 constipation-predominant IBS and 12 alternating-type IBS) and 20 age- and gender-matched controls. Gastrointestinal and psychological symptom severity and quality of life were evaluated with validated questionnaires and colonic transit time and rectal sensitivity were measured.

Results Associations detected between microbiota composition and clinical or physiological phenotypes included microbial signatures associated with colonic transit and levels of clinically significant depression in the disease. Clustering by microbiota composition revealed subgroups of IBS patients, one of which (n=15) showed normal-like microbiota composition compared with healthy controls. The other IBS samples (n=22) were defined by large microbiota-wide changes characterised by an increase of Firmicutes-associated taxa and a depletion of Bacteroidetes-related taxa.

Conclusions Detailed microbiota analysis of a well-characterised cohort of IBS patients identified several clear associations with clinical data and a distinct subset of IBS patients with alterations in their microbiota that did not correspond to IBS subtypes, as defined by the Rome II criteria.


  • Funding This study was supported by a Science Foundation Ireland CSET award to the Alimentary Pharmabiotic Centre, by the (Government of Ireland) Department of Agriculture Fisheries and Food/Health Research Board FHRI award to the ELDERMET project, by the Swedish Medical Research Council (grants 13409, 21691 and 21692), by the Marianne and Marcus Wallenberg Foundation and by the Faculty of Medicine, University of Gothenburg. MJC is supported by a fellowship from the Health Research Board of Ireland.

  • Competing interests None.

  • Patient consent Obtained.

  • Ethics approval This study was approved by the Regional Ethical Review Board at the University of Gothenburg.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data sharing statement All sequence reads are deposited at MG-RAST (accession numbers pending).

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