Getting better with a little help from our 'micr...( PASADENA Calif.-- A naturally occurr...)

PASADENA, Calif.-- A naturally occurring molecule made by symbiotic gut bacteria may offer a new type of treatment for inflammatory bowel disease, according to scientists at the California Institute of Technology.

"Most people tend to think of bacteria as insidious organisms that only make us sick," says Sarkis K. Mazmanian, an assistant professor of biology at Caltech, whose laboratory examines the symbiotic relationship between "good" bacteria and their mammalian hosts. Instead, he says, "bacteria can be beneficial and actively promote health."

For example, the 100 trillion bacteria occupying the human gut have evolved along with the human digestive and immune systems for millions of years. Some harmful microbes are responsible for infection and acute disease, while "other bacteria, the more intelligent ones, have taken the evolutionary route of shaping their environment by positively interacting with the host immune system to promote health, which gives them an improved place to live; it's like creating bacterial nirvana," says Mazmanian.

If bacteria are actively modifying the gut, their work would have to be mediated by molecules. In their recent work, Mazmanian and his colleagues have identified one such molecule, a sugar called polysaccharide A, or PSA, which is produced by the symbiotic gut bacterium Bacteroides fragilis. They have termed this molecule a "symbiosis factor," and predict that many other bacterial compounds with diverse beneficial activities await discovery.

To identify the molecule and its action, the scientists used experimental mice and induced changes to their intestinal bacteria by exposing them to a pathogenic bacterium called Helicobacter hepaticus. This microbe causes a disease in the mice that is similar to Crohn's disease and ulcerative colitis. However, when the animals were co-colonized with B. fragilis, they were protected from the disease--as were animals that were given oral doses of just
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