THIS STORY HAS BEEN FORMATTED FOR EASY PRINTING

Use of antibiotics repeatedly can alter beneficial gut germs

By Lauran Neergaard
Associated Press / September 15, 2010

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WASHINGTON — Antibiotics can temporarily upset your stomach, but now it turns out that repeatedly taking them can trigger long-lasting changes in all those good germs that live in your gut, raising questions about lingering ill effects.

Nobody knows if that leads to health problems later. But the finding is the latest in a flurry of research raising questions about how the customized bacterial zoo that thrives in our intestines forms — and whether the wrong type or amount plays a role in ailments from obesity to inflammatory bowel disease to asthma.

Don’t be grossed out: This is a story in part about, well, poop. Three healthy adults collected weeks of stool samples so that scientists could count exactly how two separate rounds of a fairly mild antibiotic caused a surprising population shift in their microbial netherworld — as some original families of germs plummeted and other types moved in to fill the gap.

It’s also a story of how we coexist with trillions of bacteria, fungi, and other microbes in the skin, nose, digestive tract, what scientists call the human microbiome.

Many are beneficial, even indispensable, especially the gut bacteria that play an underappreciated role in overall health.

“Gut communities are fundamentally important in the development of our immune system,’’ explained Dr. David Relman of Stanford University, who led the antibiotic study published Monday in Proceedings of the National Academy of Sciences. “Let’s not take them for granted.’’

Next, Relman plans to track whether antibiotics used during the first year or two of life, when youngsters form what will become their unique set of gut bacteria, seem to predispose children later to immune-related diseases.

Antibiotics already should be used cautiously because they can spur infection-causing bacteria to become drug-resistant. The new research raises different questions about effects on beneficial bacteria.

“We should start paying attention to this,’’ said Dr. Martin Blaser, a microbiome specialist at New York University Langone Medical Center, who was not involved with Relman’s work but also is planning to study the issue in children. “The main point is that antibiotic use is not free in a biological sense.’’

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