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Scientists Show How Treatment-Resistant Bacterial Infections May Form

Bacterial “clumping” wards off effects of antibiotics (Aug. 15)

New research may help explain why hundreds of thousands of Americans get sick each year — and tens of thousands die — after bacteria get into their blood. It also suggests why some of those bloodstream infections resist treatment with even the most powerful antibiotics.

According to an announcement issued on August 15, researchers at the University of Michigan have demonstrated that bacteria can form antibiotic-resistant clumps in a short time, even in a flowing liquid such as the blood.

The researchers made the discovery by building a special device that closely simulates the turbulence and forces of blood flow, and by adding a strain of bacteria that is a common cause of bloodstream infections. Tiny aggregates, or clumps, of 10 to 20 bacteria formed in the flowing liquid within 2 hours — about the same time it takes human patients to develop infections.

The researchers also showed that these clumps formed only when certain sticky carbohydrate molecules were present on the surface of the bacteria. The clumps persisted even when two different types of antibiotics were added — suggesting that sticking together protects the floating bacteria from the drugs’ effects.

When the researchers injected the clumps into mice, the clumps stayed intact even after making several trips through the bloodstream. The clumps — about the size of a red blood cell — appeared to survive the filtering that normally takes place in the smallest blood vessels and that defends the body against invaders.

The study was published in the Journal of Infectious Diseases.

For more information, visit the University of Michigan Health System Web site.

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