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25-10-2011 | Cardiology | Article

Some staphylococcus strains more likely to infect cardiac prostheses than others


Free abstract

MedWire News: Some strains of Staphylococcus aureus are more likely to infect implanted cardiac devices than others, suggest study findings.

"The question was, 'are all S. aureus created equal when binding with fibronectin?' and the answer is no," commented study author Vance Fowler from Duke University in Durham, North Carolina, USA, in a press statement.

"We identified differing S. aureus isolates from the blood of patients. All of the patients had S. aureus, 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."

As reported in the journal PNAS, the team assessed the ability of 80 different clinical isolates of S. aureus to bind to a fibronectin coated surface, as might be found on an implanted cardiac device.

The strains were obtained from 26 people who had infected cardiac devices (cultured from the device surface on removal), 20 with uninfected cardiac devices (cultured from blood samples), and 34 asymptomatic individuals without cardiac devices (cultured from nose swabs).

Fowler and co-researchers found that the S. aureus isolates taken from patients with infected devices had a "distinct binding-force signature" and unique single nucleotide polymorphisms in the gene encoding fibronectin-binding protein A (E652D, H782Q, and K786N) compared with the other isolates.

"This the first step in biofilm-based disease work," commented Fowler.

"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."

In the same statement, co-author Steven Lower (Ohio State University, Columbus, USA) said: "We often hear that nanoscience will make the world a better place, and our study demonstrates a direct correlation between something that occurs at the scale of a nanometer (i.e. a bond between a bacterium and implant) and the health of human patients with cardiovascular implants."

He added: "Some practical implications of this research could be a new protocol to determine risk of serious biofilm-related infections for patients with prostheses or patients who are considering surgical implants. For example, we could obtain a culture of S. aureus from the skin of a patient, and determine the risk of a biofilm-based infection, using the methods we described."

By Helen Albert

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