By Nicolle Charbonneau
HealthScout Reporter

Doctors in Los Angeles think they may have found a cause of the most commonly diagnosed gastroenterological disease.

Researcher at Cedars-Sinai Medical Center report that irritable bowel syndrome (IBS) may result from an overgrowth of bacteria in the small intestine, and that a small trial reveals that antibiotic therapy to kill the bacteria erased the symptoms of the disease in half the patients tested. The findings, while still preliminary, open up avenues of research toward a cure for this debilitating digestive disease.

IBS affects about 15 percent to 20 percent of the general population. It's sometimes referred to as spastic colon, mucous colitis, spastic colitis, nervous stomach or irritable colon. Until now, research hasn't raised any possible causes, but triggers are thought to include diet and stress.

Patients experience cramping, pain, gassiness, bloating, loose or more frequent bowel movements, diarrhea, or constipation. Beyond the physical and psychological impact of the disease, it also has a financial cost: It's estimated that $8 billion is spent each year on tests and treatments for this condition.

"The treatments thus far have been directed basically at the symptoms, but not at the cause, because that has been -- to date -- unknown," says lead author Dr. Mark Pimentel, the assistant director of the Cedars-Sinai Gastrointestinal (GI) Motility Program in Los Angeles.

The idea for the study, which appears in the American Journal of Gastroenterology, developed because Pimentel and his colleagues noticed that in virtually every case of IBS, patients complained of bloating. Gas in the GI tract can only get there in one of two ways, either by swallowing air or from bacteria that ferment food and produce gas. Since the amount of air that a person would have to swallow to produce bloating would immediately be belched out, it pointed toward the bacteria theory.

The next step was a lactulose hydrogen breath test for 202 patients at the GI Motility Program. Each patient would swallow a syrup of lactulose, a sugar that's indigestible to humans but tantalizing to bacteria. By measuring how long before bacteria began to break down lactulose and produce hydrogen gas, the researchers could estimate how far down in the GI tract the action was taking place, in other words, whether it was in the small intestine or the colon.

In 78 percent of the patients, gas production pointed to extreme bacterial overgrowth in the small intestine. The patients were then treated with a 10-day course of antibiotics. Of the 47 people who returned for a follow-up breath test, 48 percent no longer had any symptoms of IBS. Others experienced marked reductions in their symptoms.

Patients told Pimentel that it was the best they'd felt in a decade, and some wondered why it had taken so long. "IBS is a chronic problem," says Pimentel, one that can be debilitating both socially and psychologically. "It's a bowel condition, and people don't like to talk about their bowels. It's somewhat embarrassing."

"All the other studies that have ever been done for treating IBS have never looked at whether people were cured of their IBS," says Pimentel. "This is the first [to suggest that] bacterial overgrowth may be the potential cause."

Pimentel is now trying to determine why these patients suffer from bacterial overgrowth. Normally, there are 300-400 types of bacteria in the colon, at a concentration of roughly 1 trillion bacteria for every milliliter of stool. However, the small intestine should have less than 1,000 bacteria per milliliter of stool.

"There are various mechanisms to prevent bacteria from building up in the small intestine, except in IBS, they've got this bacterial overgrowth," says Pimentel. Stomach acid and pancreas and bile juices inhibit bacterial growth, and a valve ordinarily prevents stool from backing up into the small intestine from the colon.

White blood cells and contractions of the intestines that "clean up" between meals are also meant to prevent bacterial overgrowth. "We don't know which of these mechanisms is dysfunctional, and we're working on that eagerly in the next 12 months."

There is no single antibiotic that could kill all the strains of bacteria at work in these patients, and long-term antibiotic use raises the problem of antibiotic resistance. For that reason, Pimentel is at work on non-antibiotic therapies for future studies.

What To Do

Don't run to the doctor for a hefty dose of antibiotics just yet; researchers still have a lot of work ahead of them before declaring this a definite treatment.

You can learn more about IBS from the International Foundation for Functional Gastrointestinal Disorders and Digestive and Kidney Diseases.

You can also check out more Health Information.