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Fall 2009 Table of Contents

Combating Diarrheal Diseases

School of Medicine researchers help ID structure of bacterium that causes traveler’s diarrhea

| From Explorations | By Gina M. Digravio

An electron micrograph of an enterotoxigenic Escherichia coli bacterium, which causes traveler’s diarrhea. The bacterium has hundreds of surface fibers that attach to the intestine. Each fiber is made of proteins, including a specialized protein at the tip (shown in pink on the right) and about a thousand copies of another protein (two shown in yellow and the rest in blue) that form a springlike fiber.

Anyone who’s had traveler’s diarrhea knows that one small bug can spoil many big plans. That same bug, a strain of bacteria called enterotoxigenic Escherichia coli (ETEC), is capable of wreaking more serious havoc: it’s the leading cause of community-acquired childhood diarrhea in the developing world, according to the World Health Organization. All told, ETEC sickens hundreds of millions of people each year.

Researchers at the School of Medicine, the Naval Medical Research Center, and the National Institutes of Health have now figured out how the bacteria stick around long enough to cause diarrheal diseases, a discovery that has important implications for creating better therapeutics. The researchers have mapped the structure of the thin, hairlike fibers, called pili or fimbriae, that extend from the surface of bacteria and attach the bug to epithelial cells lining the intestine.

“Each fiber is made of proteins, including a specialized protein at the tip that does the binding, and about a thousand copies of another protein that forms a springlike fiber that can unwind and rewind during the churning motion bacteria must endure to remain bound in the gut long enough to cause disease,” says Esther Bullitt, a MED associate professor of physiology and biophysics and the study’s senior author.

The researchers believe that their newfound knowledge of the proteins — particularly the specialized tip protein — will guide the development of a vaccine. The study appeared in the June issue of the Proceedings of the National Academy of Sciences.

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