The Link Between Irritable Bowel Syndrome and Bacteria

Though Irritable Bowel Syndrome (IBS) is among the most common medical problems in the country - affecting an estimated 20 percent of the population - it's not a disease you're likely to find celebrities speaking out for - probably for fear they are as likely to become fodder for late night TV as they are to raise awareness and money for research.

And while not life-threatening, IBS is certainly life-altering, drastically affecting the day-to-day activities of the millions who suffer with it. It's a disease that's worth raising awareness about.

The cause of IBS has been elusive. It's been blamed on a host of psychological disorders, the connection between the brain and the gut, the neurotransmitter serotonin, hormones, medication, food poisoning and many other potential causes.

Researchers have built a strong case that bacteria may be the actual culprit. Mark Pimentel, M.D., a colleague of mine at Cedars-Sinai Medical Center who heads the GI Motility Program, has spent the last decade studying IBS, specifically the role bacteria may play in causing the condition. He and his colleagues unveiled the results of a large clinical study during Digestive Disease Week earlier this year in New Orleans. This study showed an antibiotic is effective in providing long term relief of IBS symptoms - excellent news for a large number of IBS sufferers.

One of the challenges with IBS is that it varies drastically from patient to patient in symptoms, severity and response to treatment. IBS patients are often categorized as having "diarrhea predominant," "constipation predominant" or a combination of both. In addition to those symptoms, IBS patients often experience abdominal pain, bloating, gas, harder or looser stools than normal and a visibly distended abdomen.

Because the symptoms can be embarrassing to talk about, many who suffer with the condition don't seek help for it, though their symptoms may be bad enough to cost time at work or school, and with family and friends.

Traditionally, treatment for IBS has focused on alleviating the symptoms. One of the reasons the treatment discovered by Dr. Pimentel and his colleagues is exciting is because it seems to strike at a cause of IBS: the relief extended well after patients stopped taking the medication. In fact, the relief extended for up to three months later.

The double-blind studies included more than 1,200 patients with diarrhea-predominant IBS at multiple centers across the nation. About 40 percent of the patients who took rifaximin, a nonabsorbable antibiotic that stays in the gut, showed sustained relief during the two weeks they took the drug and during the 10-week follow-up period. The safety profile of rifaximin was similar to placebo. Rifaximin is currently FDA-approved to treat traveler's diarrhea and hepatic encephalopathy (a condition in which there is a buildup of toxins from a failing liver).

The U.S. Food and Drug Administration is currently reviewing the relevant data and considering expanding the uses of rifaximin to include treatment of non-constipation IBS as well as IBS-related bloating. The FDA is expected to complete its review in March.

Another tactic for treating IBS is to use medications that either slow down the digestive system to treat diarrhea or speed up the digestive process to relieve constipation. And while rifaximin is not the answer for constipation-predominant IBS, bacteria are still the likely driving force. Previous research at Cedars-Sinai linked bacterial fermentation to bloating by giving patients a breath test. Patients essentially blow into a bag, and then their breath is analyzed for the level of hydrogen and methane - gases produced by specific bacteria. Constipation-predominant IBS patients tend to test positive for methane, indicating they have small intestinal bacterial overgrowth - or SIBO.

The small intestine usually contains a relatively small number of bacteria compared to the colon. In SIBO, there are not only an abnormally large number of bacteria, but the types of bacteria tend to be those that are found in the colon. The muscular activity of our intestines propels food from our stomach and through the digestive system. Even when there is no food in the small intestine, muscular activity sweeps through the tract from stomach to colon. These cleaning sweeps are also important for moving bacteria out of the small intestine. Conditions that interfere with this muscle activity can result in SIBO.

Another study by Dr. Pimentel and his colleagues, first reported in 2009, discovered a toxin present in some bacteria that causes food poisoning appears to specifically contribute to IBS. The toxin - called cytolethal distending toxin, or CDT - appears to affect the nerve cells that control the muscles in the gut, weakening the "cleaning waves" and leading to the chronic problems of IBS.

There are millions of bacteria in our body, and these gut flora are a rich new frontier for scientific research and discovery. Gut flora in particular have been of great interest to the scientific community in recent years - and to the general public, as evidenced by the growing popularity of probiotics. Unlocking understanding of these bacteria is giving scientists new insights into ailments including obesity. In the case of IBS, it's led to the best treatment for the disease yet.