Genetic Difference İn Staph İnfects Some Heart Devices, Not Others

Infectious films of staph bacteria that collect around an implanted cardiac device, such as a pacemaker, often force a second surgery to replace the device at a cost of up to $100,000. But not all implanted cardiac devices become infected. Now researchers from Duke University Medical Center and Ohio State University (OSU) have discovered how and why certain strains of staphylococcus aureus (SA) bacteria, the leading cause of these device infections, have infected thousands of implanted cardiac devices. About 4 percent of the one million annually implanted devices become infected.

The researchers examined SA's ability to bind to a sticky human (mammalian) substance called fibronectin that circulates in blood and sticks to the surfaces of implanted devices, like pacemakers.

Staph bacteria have fibronectin-binding molecules and bind to the human protein to establish an infection on the implanted medical device. Once established, these infections are difficult or impossible to eradicate without removing the device itself.

"This the first step in biofilm-based disease work," said Vance Fowler, MD, MHS, an associate professor of infectious diseases in the Duke Department of Medicine and co-corresponding author of the study. "I would expect the findings would be relevant for most implanted devices. The difference is that the cardiac devices are in direct contact with the bloodstream, and thus with fibronectin, so we need to do further work to clarify."

The study appears online in the Proceedings of the National Academy of Sciences.

"The question was, 'are all SA created equal when binding with fibronectin?' and the answer is no," Fowler said. "We identified differing SA isolates from the blood of patients. All of the patients had SA, but some of the cardiac devices were infected and some were not, and we wanted to learn why. Most people had the infection but a lucky few didn't."