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Good Can Come From Bad Bacteria

The stomach bacterium Helicobactor pylori can cause ulcers and has been linked with stomach cancer. But its presence in children may protect them from asthma, which is typically caused by a hypersensitive immune response. Eric Libby reports.

Although there are many types of bacteria in our intestines and colon, the stomach has long been dominated by H. pylori. But that is changing.

A century ago, almost everyone had H. pylori, says Martin Blaser of New York University's School of Medicine. Now, due to antibiotics, only about five percent of American children have it, he says.

Blaser explains that people usually get the bacteria from family members, especially their mothers. So, if mothers somehow lose the organism, they can't pass it on to their children.

In a study released last year, Blaser found that H. pylori in the stomach is associated with a lower risk for developing asthma.

Following up on that earlier work, Blaser and his colleagues looked at a government study of the health and nutrition of 7,000 Americans from 1999 to 2000. What he found not only confirmed the earlier report but also extended it. "There was in fact, again, an inverse relationship between H. pylori and childhood asthma," he says, "and, we also found, childhood hay fever as well."

Blaser stresses that his work has not determined whether H. pylori is actually protecting children from asthma or if it is just a consequence of the protection. Still, he points out that in his earlier study, the strains of H. pylori associated with the most protection (cag A positive) have an interesting ability.

"[This] H. pylori [strain] has a way of injecting its own proteins into human cells that line the stomach. It's been called a molecular syringe. And they change the patterns and the pathways cells use to do their work."

This might cause the body to relax its immune response, reducing the risk of developing asthma.

In future studies, Blaser and his colleagues hope to determine if and how H. pylori provides protection.

Their work is published in the July 15 online issue of The Journal of Infectious Diseases.