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

Staphylococcus aureus is a common bacteria that's mostly pretty harmless, but certain strains can cause more problems. Methicillin-resistant Staphylococcus aureus (MRSA) is a particularly troublesome bug that's most dangerous to people whose immune systems are already compromised, meaning it can wreak havoc in hospitals and retirement homes. Unfortunately it's getting harder and harder to treat – it's not just resistant to methicillin as its name suggests, but also an ever-growing list of other common antibiotics.

New antibiotics are in the works, but of course eventually bacteria will inevitably develop resistances to those too. So scientists are trying to find longer-term solutions that superbugs won't be able to adapt to, such as material surfaces that tear them apart or nanoparticles that produce toxic molecules when triggered by light.

In a similar vein, the Purdue researchers have developed their own form of light therapy. The team found that MRSA can be weakened through "photobleaching" – essentially sapping the color of the bacteria by exposing it to blue light. Since these pigments are part of how the bugs can infect a host, this can reduce their ability to cause harm.

"When you bleach something in the wash machine, you're extracting the color using chemicals," says Mohamed Seleem, an author of the study. "What we're doing here is similar, but we're using blue light."

The light itself isn't killing the MRSA – instead, it lowers its defenses enough for drugs and other molecules to finish it off, even those that the bugs would normally be resistant to. In tests on mice with MRSA-infected wounds, the researchers found that mild antiseptics like hydrogen peroxide were effective at destroying 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 would take the form of a small box with a light in it, which shines through a hole onto the wound. Importantly, the light has been found to be safe on mammalian cells.

"This new tool can treat any superficial wound infected with MRSA, which are typically very difficult to treat," says Seleem. "The device itself is very small and easy to use. We're hoping that in the next few years, anyone could carry it around in their purse."

The research was published in the journal Advanced Science.

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