Study in mice shows how bacteria protect against bowel disease

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TORONTO - With upwards of 1,000 species of bacteria teeming in your gut, odds were good this intestinal jungle did more than digest food and fight harmful organisms.

Scientists now have the findings of a study that show how one strain of friendly bacteria protects the health of its human host. And experts say it suggests gut microflora is an untapped resource that could reveal new therapies to fight human diseases.

In a study released in the journal Nature, U.S. researchers describe how a common strain of bacteria, called Bacteroides fragilis, offers protection against inflammatory bowel disease in mice.

They found a single molecule produced by the bacteria can shut down the intestinal inflammation that causes the animals to get inflammatory bowel disease, a condition which includes Crohn's disease and ulcerative colitis.

Previous studies revealed the bacteria is important for immune function in animals. But the authors say this is the first study to describe how a molecule produced by "good" intestinal bacteria works to prevent disease in animals.

The finding has exciting implications for future research into gut microflora, says Dennis Kasper, study co-author and professor of medicine, microbiology and molecular genetics at Harvard Medical School.

"Here we have a reservoir of unknown organisms each with its own unknown molecules," he says. "The gut may be a vast warehouse or storehouse for potential therapeutics that we don't know about."

To investigate the bacteria's potential, Kasper and his colleagues used special mice bred to have no intestinal microbes. Animals that were fed an intestinal bacteria, called Helicobacter, developed inflammatory bowel disease. But animals that received a combination of Helicobacter and the beneficial bacteria, B. fragilis, were fine.

Further experiments revealed a specific sugar molecule produced by the beneficial bacteria, called polysaccharide A, prompted the immune system to launch an anti-inflammatory response, which prevented inflammatory bowel disease from flaring up.

Dr. Brian Feagan, director of the clinical trials group at the Robarts Research Institute, University of Western Ontario, calls the study important because it pinpoints a specific bacteria-controlled mechanism that regulates inflammation.

"This holds promise for a very specific low-toxic, or non-toxic, therapy that is based on flora found in the guts," says Feagan, an expert on inflammatory bowel disease.

Canada has one of the highest rates of the disease in the world, he says, with roughly 200 people per every 100,000 diagnosed with Crohn's disease or ulcerative colitis.