Sunscreen ingredient may prevent medical implant infections

A common ingredient used in sunscreen could be an effective antibacterial coating for medical implants such as pacemakers and replacement joints, researchers have found.
A coating of zinc oxide nanopyramids can disrupt the growth of methicillin-resistant Staphylococcus aureus (MRSA), reducing the film on treated materials by over 95 per cent.
About a million implanted medical devices are infected each year with MRSA and other bacterial species.
"It is extremely difficult to treat these infections," said J Scott VanEpps, a clinical lecturer and research fellow in the University of Michigan Medical School in US.
Treatment involves either a long course of antibiotics, which can lead to antibiotic resistance and toxic side-effects, or the implants must be surgically replaced, which can be quite extensive for devices such as heart valves and prosthetic joints, VanEpps said.

Ideally, doctors would like to prevent the infections from occurring in the first place. One option is to coat the devices with something that bacteria can not grow on.

The new result suggest that such a coating could be made from nanoparticles of zinc oxide - a common sunscreen and diaper rash cream ingredient.
If the nanoparticles are shaped like a pyramid with a hexagon-shaped base, they are very effective at preventing an enzyme called beta-galactosidase from breaking down lactose into the smaller sugars glucose and galactose, which the bacteria use for fuel.
Shape is important, both for the enzyme and for the nanoparticles. The enzyme needs to be able to twist in order to cut the lactose into the smaller sugars.

Two amino acids, or protein building blocks, sit opposite one another across a groove in the enzyme. The lactose fits into the groove, and the amino acids come together to catalyse the breakup into glucose and galactose.
"Although more studies need to be carried out, we believe that zinc oxide nanopyramids interfere with this twisting motion," said Nicholas Kotov, Professor of Chemical Engineering, whose group made the nanoparticles.
The team found that part of the nanoparticle - an edge or the point - inserts itself into the groove. By clogging up just one of the four grooves, the nanoparticles can shut down the whole enzyme by preventing the twisting action.

The researchers covered some pegs with the nanopyramids and then VanEpps' team stuck them into a substance that would allow bacteria to grow.
They evaluated four species of bacteria on coated and uncoated pegs - two staphylococcal species (including MRSA), one species that causes pneumonia and E coli.
After 24 hours of growth, the number of viable staphylococcal cells recovered from the coated pegs was 95 per cent less than those from the uncoated pegs. The pneumonia and E coli species were less susceptible to the nanoparticles.
The study was published in the journal Nanomedicine.