How antibiotic-resisting bacterial infections may form

New research may help explain why hundreds of thousands of Americans a year get sick – 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.

In a new paper in the Journal of Infectious Diseases, a team of University of Michigan researchers demonstrate 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 adding a strain of bacteria that's a common cause of bloodstream infections.

Tiny aggregates, or clumps, of 10 to 20 bacteria formed in the flowing liquid in just two hours – about the same time it takes human patients to develop infections.

The researchers also showed that these clumps only formed 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, they stayed intact even after making many 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 defends the body against invaders.