Gut 56:802-808 doi:10.1136/gut.2006.108712
  • Neurogastroenterology

Small intestinal bacterial overgrowth in patients with irritable bowel syndrome

  1. Iris Posserud,
  2. Per-Ove Stotzer,
  3. Einar S Björnsson,
  4. Hasse Abrahamsson,
  5. Magnus Simrén
  1. Department of Internal Medicine, Sahlgrenska University Hospital, Göteborg, Sweden
  1. Correspondence to:
    M Simrén
    Section of Gastroenterology and Hepatology, Department of Internal Medicine, Sahlgrenska University Hospital, 41345 Göteborg, Sweden; magnus.simren{at}
  • Accepted 22 November 2006
  • Revised 14 November 2006
  • Published Online First 5 December 2006


Background: Small intestinal bacterial overgrowth (SIBO) has been proposed to be common in irritable bowel syndrome (IBS), with altered small-bowel motility as a possible predisposing factor.

Aim: To assess the prevalence of SIBO, by culture of small-bowel aspirate, and its correlation to symptoms and motility in IBS.

Methods: 162 patients with IBS who underwent small-bowel manometry and culture of jejunal aspirate were included. Cultures from 26 healthy subjects served as controls. Two definitions of altered flora were used: the standard definition of SIBO (⩾105 colonic bacteria/ml), and mildly increased counts of small-bowel bacteria (⩾95th centile in controls).

Results: SIBO (as per standard definition) was found in 4% of both patients and controls. Signs of enteric dysmotility were seen in 86% of patients with SIBO and in 39% of patients without SIBO (p = 0.02). Patients with SIBO had fewer phase III activities (activity fronts) than patients without SIBO (p = 0.08), but otherwise no differences in motility parameters were seen. Mildly increased bacterial counts (⩾5×103/ml) were more common in patients with IBS than in controls (43% vs 12%; p = 0.002), but this was unrelated to small intestinal motility. No correlation between bacterial alterations and symptom pattern was observed.

Conclusions: The data do not support an important role for SIBO according to commonly used clinical definitions, in IBS. However, mildly increased counts of small-bowel bacteria seem to be more common in IBS, and needs further investigation. Motility alterations could not reliably predict altered small-bowel bacterial flora.


  • Published Online First 4 December 2006

  • Funding: This study was supported by the Swedish Medical Research Council (grant number 13409), and by the Faculty of Medicine, University of Göteborg.

  • Competing interests: None.