Key sunscreen ingredient may halt infection

Thursday, November 19, 2015 - 7:29pm

In the hands of University researchers, sunscreen may do more than just protect our skin: It might also protect our medical devices from bacteria that kill more than 100,000 Americans every year.

In a paper published Oct. 27, a University research team showed that coating objects with nanoparticles of zinc oxide, a key ingredient in sunscreen, reduced the growth of a species of antibiotic-resistant bacteria by 95 percent.

In hospitals, where antibiotics are used extensively, particularly dangerous bacteria like methicillin resistant Staphylococcus aureus — or MRSA — evolve because they are able to survive antibiotic treatments. If these bacteria get on objects like replacement joints, artificial heart valves or screws used with common athletic injuries, they can multiply inside a patient’s body and cause severe infections that can’t easily be cured with antibiotics.

If bacteria can’t grow on the objects in the first place, however, antibiotic resistance poses less of a problem. This is where the zinc oxide nanoparticles could help.

Medical School Lecturer J. Scott VanEpps, head of the research team that presented the findings, said the field of antibacterial coatings is important because of its life-saving implications.

“About a million medical devices are infected every year,” VanEpps said. “The best way to treat this is often to take the infected device out. It’s relatively simple if you’re removing something like a catheter. But when you’re talking about removing a heart valve or prosthetic joint, that requires a long, taxing surgery that could involve complications.”

Engineering Prof. Nicholas Kotov is head of the chemical engineering laboratory that synthesized the nanoparticles. While zinc oxide’s bacteria-fighting properties are relatively well known, examining different shapes it forms on the nanoscopic scale is an area of active research. The researchers examined whether the shape of the particles mattered, testing three different types: spheres, plates and pyramids with hexagonal bases. They produced four kinds of pegs: uncoated, coated with spheres, coated with plates and coated with hexagonal pyramids.

VanEpps’s team took pegs and put them in a bacteria-growing environment. After giving the bacteria 24 hours to grow, they found that the pegs coated with the nanopyramids had 95 percent fewer Staph bacteria — including MRSA — than the uncoated pegs.

While the researchers know that the nanopyramids could prevent these dangerous infections, how the exact process works remains undiscovered. VanEpps said the key may be the nanoparticles’ shape, which enables them to inhibit certain enzymes important for bacterial growth.

Because zinc oxide nanopyramids can inhibit multiple bacterial enzymes while antibiotics normally disrupt just one, it may be much harder for bacteria to evolve resistance against the nanoparticles.

“We’ve seen that the zinc oxide nanopyramids hinder biofilm growth, and it’s been shown that they inhibit certain enzymes. Next, we want to figure out how these two facts fit together,” VanEpps said.

The researchers plan to learn more about the nanoparticles before they can be adapted for medical use. For example, they will observe whether different concentrations of particles can inhibit other types of bacteria without harming human cells.