Brown U.: “Bacterial assassins” target staph invaders on implants

June 26, 2009: Researchers at Brown U. say they have devised a way to eliminate bacteria that invade human tissue though medical devices: send magnetic nanoparticle “headhunters” after them.

Their findings, published in the International Journal of Nanomedicine, address the problem of Staphylococcus epidermidis, a bacteria commonly found on human skin and generally innocuous — unless it gets inside the body; it’s one of the leading causes of infections in hospitals. Among the various ways s. epidermis gets into the body is by “hitching a ride” on medical device implants, e.g. catheters, prostheses, etc. Once inside, the bacteria multiply on the device’s surface and generate a slimy film that wards off antibiotics — up to 2.5% of hip and knee implants in the US thus become infected.

To do battle, Brown researchers Thomas Webster and Erik Taylor focused on superparamagnetic iron-oxide nanoparticles (8nm-high, and chosen for magnetic maneuverability and trackability) to zero in on the implant. Once there the nanoparticles penetrate the bacterial shield (they speculate that a strong enough magnetic field forces them through); once inside the defenses the particles penetrate the bacterial cells and kill them in an as-yet unknown process. (Iron was known to kill s. epidermis, but Webster speculates it may be due to iron overload in the bacteria cell.) After 48hrs, 10μg of the agents were seen to eliminate up to 28% of the bacteria; in three treatments over six days, essentially all of them were destroyed, indicating “a continual killing of the bacteria until the film is gone,” noted Webster.

Next steps are to see how the iron-oxide nanoparticles fare against other bacteria, and then eventually move the research into trials with implants in animals. And they also want to better understand something else they saw as a result of the nanoparticle infusion — promotion of natural bone cell growth on the implant’s surface.

The research was funded by the private Hermann Foundation and in part by the National Science Foundation.

Iron-oxide nanoparticles developed at Brown University target an infected prosthesis, penetrate a bacterial film on the implant’s surface and thwart the colony by killing the bacteria. The nanoparticles also are believed to help natural bone cell growth. (Credit: Erik Taylor/Brown University)


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