Treatment for Bacterial Overgrowth in the Irritable Bowel Syndrome

Over the last 10 to 20 years, the irritable bowel syndrome (IBS) has garnered considerable scientific interest. The acceptance of the biopsychosocial model (1), the application of symptom-based diagnostic criteria (for example, Rome diagnostic criteria), and the growth in biological and behavioral measurement technology (2, 3) has created a fertile area for new research in IBS with the potential for more effective treatments. Research now focuses on altered motility and neuroenteric signaling; visceral hypersensitivity and its enhancement by inflammation and altered mucosal immunity; and brain–gut dysfunction via altered pain, autonomic, and stress-related (for example, corticotropin-releasing hormone) pathways (2, 3). It is now evident that IBS is not a single disease but is a well-characterized symptom complex that relates symptoms to a variety of underlying physiologic determinants from gut to brain and back. Thus, a single “magic bullet” for the disorder is unlikely: Treatments will be used alone or in combination to target the altered physiologic determinants that are unique to each individual.

The role of the bacterial flora, a new area of research in the clinical expression of IBS, has developed from several lines of evidence: the recognition of postinfectious IBS in susceptible hosts after bacterial gastroenteritis (4, 5); the finding of an altered colonic bacterial ecology as manifested by stool cultures in patients with IBS compared with controls (6); the potential benefit of treating IBS with probiotics, presumably to replace “bad” bacteria with “good” bacteria (for example, bifidobacteria [7, 8] and lactobacilli [8]) and reduce mucosal inflammation (9); and the evidence for small-bowel bacterial overgrowth in some patients with IBS (10–13). With regard to the latter, a research group has identified, by using lactulose H₂ breath assessment, high frequencies of bacterial overgrowth in IBS over the last several years: About 84% of …