Gold Standard Evidence that Bacterial Overgrowth is at the Heart of IBS



An overgrowth of bacteria in the gut has been definitively linked to irritable bowel syndrome (IBS), according to the results of a new study at Cedars-Sinai (Los Angeles) 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, which affects an estimated 30 million people in the US alone. Previous studies have indicated that aerobic bacteria play a role in the disease, including breath tests detecting methane – a byproduct of bacterial fermentation in the gut. But this study was the first to make the link using bacterial cultures.

The study, published May 11 by Digestive Diseases and Sciences (“The prevalence of overgrowth by aerobic bacteria in the small intestine by small bowel culture: relationship with irritable bowel syndrome”), 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, 37.5% also were diagnosed with small intestine bacterial overgrowth – SIBO [excessive bacteria of the type normally found in the colon, which ferment carbohydrates into gas] – compared to fewer than 10% of those without the disorder.

• Of those with diarrhea-predominant IBS, 60% also had SIBO.

• And of those with constipation predominant IBS, 27.3% had SIBO.

• Overgrowth of Escherichia coli, Enterococcus spp and Klebsiella pneumoniae were the most common isolates found.

• A history of type 2 diabetes and intake of proton pump inhibitors (drugs to reduce stomach acid) were also independently and positively associated with SIBO.

• Gastritis (inflammation of the stomach lining) appeared to be protective against SIBO.

“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,” says Mark Pimentel, MD, director of the Cedars-Sinai GI Motility Program and an author of the study.
Dr. Pimentel first bucked standard medical thought more than a decade ago when he suggested that bacteria played a significant role in the disease. He has led clinical trials showing that rifaximin, a targeted antibiotic that is absorbed only in the gut and not into the circulatory system, is an effective treatment for patients with IBS – and that “Patients who take rifaximin experience relief of their symptoms even after they stop taking the medication.”

“In the past, treatments for IBS have always focused on trying to alleviate the symptoms,” Dr. Pimentel adds, and “this new study confirms what our findings with the antibiotic and our previous studies always led us to believe: Bacteria are key contributors to the cause of IBS.”

The study is a collaboration with researchers at Sismanogleion General Hospital in Athens, Greece, and at the University of Athens.

Sources: Based on the study abstract and Cedars-Sinai Medical Center press release, May 25, 2012

For other reading on bacterial overgrowth in the small intestine, see for example:

“Restless Legs Syndrome is associated with Irritable Bowel Syndrome and Small Intestinal Bacterial Overgrowth,” and “Small Intestinal Bacterial Overgrowth in Patients with Interstitial Cystitis and Gastrointestinal Symptoms,” by Leonard B Weinstock, et al.

“Gut Bacteria, the H2S Test & Mitochondrial Dysfunction in ME/CFS,”  and “Fermentation in the Gut and CFS as a Protective Adaptive Response,” by Sarah Myhill, MD.

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