Bacteria and irritable bowel syndrome: The evidence for small intestinal bacterial overgrowth

Abstract

Irritable bowel syndrome (IBS) is a complex, yet common diagnosis in gastroenterology. Recent data suggest the increasing importance of bacteria in the pathophysiology of IBS. Some studies have shown that IBS can be precipitated by an acute case of gastroenteritis. These pathogenic organisms may contribute to long-term gut dysfunction. In another line of effort, a growing body of evidence links IBS to the presence of excessive bacteria in the small bowel, called bacterial overgrowth. Although the means by which this is determined have been indirect, studies demonstrating the benefit of unabsorbed antibiotics suggest that reduction in gut flora is important. Further work has also examined bacterial overgrowth in the context of the various symptoms of patients with IBS. These symptom complexes include constipation, diarrhea, and alternating forms of the condition. Although this idea seems initially counterintuitive, it has been demonstrated that the fermentation of methane in the gut is associated with and can result in the slowing of intestinal transit, resulting in constipation. In this review, these topics are discussed and outlined.

The Prevalence of Overgrowth by Aerobic Bacteria in the Small Intestine by Small Bowel Culture: Relationship with Irritable Bowel Syndrome

“…This definition was based on (a) former publications about the definition of SIBO [11], and (b) on a preliminary cohort of 15 patients undergoing upper GI tract endoscopy for mild dyspepsia. These patients had negative histories for co-morbidities and for drug intake and they did not have any finding on endoscopy.…”

Incidence of Predominant Methanogenic Flora in Irritable Bowel Syndrome Patients and Apparently Healthy Controls from North India

“…These pathogenic organisms may contribute to long-term gut dysfunction. In another line of effort, a growing body of evidence links IBS to the presence of excessive bacteria in the small bowel, called bacterial overgrowth [3].…”

New horizons for the infectious diseases specialist: How gut microflora promote health and disease

“…Furthermore, some IBS patients appear to have abnormal lactulose breath tests, implicating bacterial overgrowth as contributing to the pathogenesis of IBS [37]. A link between IBS and bacterial overgrowth is further supported by an up to 75% improvement in gastrointestinal complaints after neomycin treatment [37]. Similar improvement has been noted after treatment with rifaximin.…”

“…A recent study has demonstrated decreased levels of coliforms, lactobacilli, and bifidobacteria in the feces of IBS patients and increased anaerobes, including Bacteroides spp, in the colonic mucosa [36]. Furthermore, some IBS patients appear to have abnormal lactulose breath tests, implicating bacterial overgrowth as contributing to the pathogenesis of IBS [37]. A link between IBS and bacterial overgrowth is further supported by an up to 75% improvement in gastrointestinal complaints after neomycin treatment [37].…”