Antibiotics were one of the most important scientific discoveries of the 20th century, but their usefulness is rapidly fading. Overuse has led to bacterial resistance to the drugs, which could potentially lead us to a future where once simple infections again become life-threatening. Now, researchers at Purdue University have found that blue light can weaken a particularly nasty "superbug" and make it susceptible again to mild antiseptics.

Staphylococcus aureus is a common bacterium, most of which are harmless, but certain strains can cause more problems. Methicillin-resistant Staphylococcus aureus (MRSA) is a particularly troublesome bacterium that is most dangerous to people with already compromised immune systems, meaning it can cause serious infections in hospitals and nursing homes. Unfortunately, it has become increasingly difficult to treat - it is not only resistant to methicillin but also to a growing number of other common antibiotics.

New antibiotics are still in development, but of course, bacteria will eventually develop resistance to them as well. Therefore, scientists are working hard to find long-term solutions that superbugs cannot adapt to, such as antimicrobial materials that can quickly eliminate bacteria or photosensitive nanoparticles that can release reactive oxygen species to kill superbugs.

Similarly, researchers at Purdue University have developed their own phototherapy. The team found that MRSA can be weakened by "photobleaching" - essentially removing the color of the bacteria by exposing them to blue light. Since these pigments are part of how bacteria infect their hosts, this may reduce their ability to cause harm.

"When you bleach something in a washing machine, you use chemicals to remove color," said Mohamed Seleem, the author of the study. "What we're doing here is similar, but we're using blue light."

The light itself does not kill MRSA - instead, it lowers its defenses enough for drugs and other molecules to finish it off, even those that bacteria would normally resist. In tests on mice with MRSA-infected wounds, researchers found that mild antiseptics like hydrogen peroxide could effectively destroy bacteria weakened by blue light.

The team has patented a device that uses this technology to treat MRSA-infected wounds. The idea is that it will take the form of a small box with a light that shines through a hole onto the wound. Importantly, scientists have found that the light is safe on mammalian cells.

"This new tool can treat any surface wound infected with MRSA, which are often difficult to treat," said Seleem. "The device itself is very compact and easy to use. We hope that in the next few years, anyone will be able to carry it with them."

The study was published in the journal Advanced Science.