Irritable Bowel Linked To Gut Bacteria, Definitively

A new study of Greek patients shows that overgrowth of bacteria in the gut is definitively linked to irritable bowel syndrome (IBS). It is the first to use the "gold standard" method of examining gut bacterial cultures to connect bacteria to the cause of a disease that affects some 30 million Americans. The researchers say their findings confirm antibiotics are a successful treatment for IBS.

Previous studies have suggested a link between gut bacteria and IBS, but they have been based on testing methane (a byproduct of bacterial fermentation) in the breath.

The findings, published in the May issue of Digestive Diseases and Sciences, corroborate those of previous clinical trials at Cedars-Sinai that showed antibiotics are effective against IBS.

Study author Mark Pimentel is director of the Cedars-Sinai GI Motility Program. He commented in a statement to the press released on Friday that:

"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."

"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," he added.

For the study, Pimentel and colleagues from Sismanogleion General Hospital in Athens, Greece, and from the University of Athens, examined samples of small bowel cultures from over 320 Greek patients to confirm the presence of small intestinal bacterial overgrowth (SIBO). The patients were all scheduled to receive upper gastrointestinal (GI) tract endoscopy.

They found that more than a third of the patients with IBS had SIBO, compared with only 10% of those without IBS.

Of patients with diarrhea-predominant form of IBS, 60% had SIBO, compared to just over 27% without the diarrhea form.

The researchers used the Rome II criteria to define IBS. The Rome criteria is a system, based on clinical symptoms, of classifying disorders of the digestive system in which symptoms can't be explained through presence of tissue abnormality. As well as IBS, other disorders that are defined using Rome criteria include dyspepsia, functional constipation, and functional heartburn.

Pimentel and colleagues conclude:

"Using culture of the small bowel, SIBO by aerobe bacteria is independently linked with IBS. These results reinforce results of clinical trials evidencing a therapeutic role of non-absorbable antibiotics for the management of IBS symptoms."

IBS is the most common gastrointestinal disorder in the US. Symptoms include painful bloating, constipation, diarrhea or an alternating pattern of both.

Many people with IBS avoid social interactions because they are embarassed by their symptoms.

Ten years ago Pimentel went against the thinking of the time when he proposed bacteria played a key role in IBS. Since then he has led clinical trials that have shown rifaximin, a targeted antibiotic absorbed only in the gut, is an effective treatment for IBS.

Pimentel said in the past, treatments have focused on alleviating symptoms. But "patients 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: bacteria are key contributors to the cause of IBS," he affirmed.