Contribution of Gut Microbes to Gastrointestinal Motility Disorders

The community of microorganisms living in our intestine is ~10 times greater in number than the total number of somatic and germ cells that compose our body. Our relationship with colonizing gut microbes begins at birth. The specific constitution of this microbial community or microbiome varies between individuals and between the various regions of the gastrointestinal tract. The relationship between individual microbial species and the host ranges from commensalisms to mutualism to parasitism. Evidence increasingly confirms that the biology of gut bacteria and the human host including the motility of our gastrointestinal tract are inseparable. What happens when the balanced relationship between the human host and gut microbiota is disturbed? Recent evidence suggests that a shift in the host-gut microbial relationship as exemplified by small intestinal bacterial overgrowth (SIBO) may contribute to the pathogenesis of IBS. The results of two prospective, randomized, double-blinded, placebo-controlled studies using nonabsorbable antibiotics suggest that an antibiotic sensitive mechanism located in the small intestine is responsible for bloating and other symptoms of IBS. A 75% global symptomatic improvement was reported by IBS patients when abnormal bacterial fermentation suggesting SIBO was eliminated. Small intestinal bacterial overgrowth would be the best explanation for such a mechanism. Methane, a gaseous byproduct of microbial fermentation slows transit and is associated with constipation. These findings argue for the role of gut microbes in gastrointestinal motility disorders and the need for new diagnostic and treatment approaches directed at small intestinal bacterial overgrowth.