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Research Corner

Study pinpoints toxin likely responsible for IBS


A toxin present in some bacteria that causes food poisoning is a possible culprit behind irritable bowel syndrome, researchers in the GI Motility Program at Cedars-Sinai have found.

The research, done in a new animal model of IBS, examined cytolethal distending toxin, or CDT, which appears to affect the nerve cells that control the muscles in the gut. In this study, the investigators found that animals exposed to a food-poisoning bacteria that did not express CDT developed fewer bowel habit abnormalities. Mark Pimentel, M.D., (pictured at far right) and Christopher Chang, M.D., Ph.D., (pictured at right) are the co-primary investigators on the study.

"This is a huge step forward in understanding this disease and how to fight it," said Dr. Pimentel, director of the GI Motility Program. "Identifying the mechanism behind IBS should help us determine how to treat and cure it."

The findings were reported at the Neurogastroenterology & Motility 2009 Joint International Meeting in Chicago on Aug. 29.

IBS, which affects 20 percent of Americans annually, is an intestinal disorder that causes abdominal pain and discomfort, cramping, bloating, diarrhea and constipation. It is a long-term condition, with episodes that may be mild or severe and may be exacerbated by stress. It often begins in adolescence or early adult life.

In the animal model, 27 percent of rats with food poisoning had bacterial overgrowth in their small intestines, and those rats had fewer nerve cells to control movement of the gut. In further study, rats with a strain of food poisoning with CDT present developed bacterial overgrowth and IBS symptoms. Rats with the food poisoning strain free of CDT experienced significantly less symptoms in the long term.

This new understanding of how IBS functions is one of several important discoveries made about the disease by Dr. Pimentel and his colleagues. Previous studies showed that IBS patients benefit from antibiotic use, even after the course of treatment ended. This has become a common practice in treating the condition. Dr. Pimentel also validated a breath test that measures a level of hydrogen and methane in the breath. An abnormal level of methane has proven to be a predictor of constipation-dominant IBS.