Bacterial concepts in irritable bowel syndrome.

An overlap of symptoms in irritable bowel syndrome (IBS) exists across subtype groups. Symptoms include intestinal gas, diarrhea, dyspepsia, bloating, abdominal pain, and constipation. The unifying symptom may be excessive intestinal gas as a by-product of intestinal microbial fermentation. Abnormal fermentation of food takes place when gut microbes expand proximally into the small intestine instead of being confined predominantly to the colon. Such proximal expansion of indigenous gut microbes or small intestinal bacterial overgrowth (SIBO) may lead to activation of host mucosal immunity and an increase in intestinal permeability to result in flu-like extra-intestinal symptoms that accompany the classic IBS symptoms of altered bowels. The presence of methane on lactulose breath testing is associated with constipation-predominant IBS. Antibiotic therapy may be appropriate to treat underlying SIBO in IBS patients. Seventy-five percent improvement of IBS symptoms was reported in a double-blind, placebo-controlled study once antibiotics succeeded in treating bacterial overgrowth. Once a good clinical response and normalization of the lactulose breath test are achieved, a prokinetic agent may be used to stimulate phase III of interdigestive motility to delay relapse of bacterial overgrowth.