Physicians definitively links irritable bowel syndrome and bacteria in gut

May 25, 2012, Cedars-Sinai Medical Center

An overgrowth of bacteria in the gut has been definitively linked to Irritable Bowel Syndrome in the results of a new Cedars-Sinai study which used cultures from the small intestine. This is the first study to use this "gold standard" method of connecting bacteria to the cause of the disease that affects an estimated 30 million people in the United States.

Previous studies have indicated that bacteria play a role in the disease, including breath tests detecting – a byproduct of bacterial fermentation in the gut. This study was the first to make the link using bacterial cultures.

The study, in the current issue of Digestive Diseases and Sciences, examined samples of patients' small bowel cultures to confirm the presence of small intestinal bacterial overgrowth – or SIBO – in more than 320 subjects. In patients with IBS, more than a third also were diagnosed with bacterial overgrowth, compared to fewer than 10 percent of those without the disorder. Of those with diarrhea-predominant IBS, 60 percent also had bacterial overgrowth.

"While we found compelling evidence in the past that bacterial overgrowth is a contributing cause of IBS, making this link through bacterial cultures is the gold standard of diagnosis," said Mark Pimentel, MD, director of the Cedars-Sinai GI Motility Program and an author of the study. "This clear evidence of the role bacteria play in the disease underscores our clinical trial findings, which show that antibiotics are a successful treatment for IBS."

IBS is the most common gastrointestinal disorder in the U.S., affecting an estimated 30 million people. Patients with this condition suffer symptoms that can include painful bloating, constipation, diarrhea or an alternating pattern of both. Many patients try to avoid social interactions because they are embarrassed by their symptoms. Pimentel has led clinical trials that have shown rifaximin, a targeted antibiotic absorbed only in the gut, is an effective treatment for patients with IBS.

"In the past, treatments for IBS have always focused on trying to alleviate the symptoms," said Pimentel, who first bucked standard medical thought more than a decade ago when he suggested bacteria played a significant role in the disease. " who take rifaximin experience relief of their symptoms even after they stop taking the medication. This new study confirms what our findings with the antibiotic and our previous studies always led us to believe: are key contributors to the cause of IBS."

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