Sweet chestnut tree leaves contain chemicals that can tame the MRSA superbug, research has shown.
The compounds "disarm" Staphylococcus aureus bacteria and stop them producing harmful toxins, say scientists.
Yet they do not appear to boost levels of drug resistance.
Traditional folk remedies based on chestnut leaves inspired the US team at Emory University.
Lead researcher Dr Cassandra Quave said: "We've identified a family of compounds from this plant that have an interesting medicinal mechanism.
"Rather than killing staph, this botanical extract works by taking away staph's weapons, essentially shutting off the ability of the bacteria to create toxins that cause tissue damage. In other words, it takes the teeth out of the bacteria's bite."
The chestnut extract was even effective against the superbug Staphylococcus strain MRSA (methicillin-resistant Staphylococcus aureus), healing mice with serious skin infections.
For years the Emory team had investigated the traditional remedies of rural people in southern Italy and other parts of the Mediterranean.
Detective work by the researchers led them to the European sweet chestnut tree, Castanea sativa.
"Local people and healers repeatedly told us how they would make a tea from the leaves of the chestnut tree and wash their skin with it to treat skin infections and inflammations," said Dr Quave.
In the laboratory, the scientists steeped chestnut leaves in solvents to extract 94 chemicals including the anti-bacterial ursene and oleanene compounds.
A single 50 microgram dose of the extract cleared up MRSA skin infections in laboratory mice, halting damage to tissue and red blood cells.
Lab dish tests showed that the compounds did not harm skin cells or bacteria that live harmlessly on the skin, the researchers reported in the online journal Public Library of Science ONE.
The university's Office of Technology Transfer has filed a patent on the extract's unique properties. The scientists are now looking at its individual components to see if they work best in combination or alone.
Potential applications include a protective spray for athletic equipment, coatings for medical devices and personal products such as tampons, and as a treatment for MRSA.
Dr Quave said: "Many pharmaceutical companies are working on the development of monoclonal antibodies that target just one toxin. This is more exciting because we've shown that with this extract, we can turn off an entire cascade responsible for producing a variety of different toxins.
"It's easy to dismiss traditional remedies as old wives' tales, just because they don't attack and kill pathogens, but there are many more ways to help cure infections, and we need to focus on them in the era of drug-resistant bacteria."