Brown Engineers Discover Staph-Fighting Ability of Selenium

A team of engineers at Brown University (Providence, RI) report that they have coated polycarbonate, a material commonly used to manufacture catheters and endotracheal tubes, with selenium nanoparticles to combat bacteria. They have found that the selenium coating significantly reduces the growth of Staphylococcus aureus, sometimes by as much as 90%. "The longer we can delay or inhibit completely the formation of these colonies, the more likely your immune system will clear them," remarks Thomas Webster, a Brown University professor of engineering and orthopedics who studies how nanotechnology can improve medical implants. "Putting selenium on there could buy more time to keep an endotracheal tube in a patient."

Webster and first author Qi Wang grew selenium nanoparticles of two different size ranges and then used solutions of them to coat pieces of polycarbonate using a quick, simple process. On some of the polycarbonate, they then applied and ripped off tape not only to test the durability of the coatings but also to see how a degraded concentration of selenium would perform against bacteria.

After creating both types of coated surfaces, the researchers measured the concentration of nanoparticles using electron and atomic force microscopes to determine how much surface area of selenium was exposed to interact with bacteria. After the tape test, they discovered, smaller nanoparticles adhered better to the polycarbonate than larger ones. Then the engineers exposed both coated and uncoated pieces of polycarbonate to cultured staph bacteria. Among the coated pieces, some had the larger nanoparticles and some had the smaller ones. While some of these pieces had been degraded by the tape, others had not.

The researchers found that all four types of selenium coatings proved effective in reducing staph populations after 24, 48, and 72 hours compared with the uncoated controls. Reductions larger than 90% after 24 hours and as much as 85% after 72 hours were found on polycarbonate with coatings containing particles of either size range that had not been degraded by the tape. Among those coatings that had been subjected to the tape test, the smaller nanoparticle coatings proved more effective.

Staph populations exposed to any of the coated polycarbonate pieces peaked at 48 hours, perhaps because that is when the bacteria could take fullest advantage of the in vitro culture medium. But levels always fell back dramatically by 72 hours.