European chestnut tree leaves contain ingredients with the ability to disarm dangerous staph bacteria without boosting its drug resistance, scientists have revealed. The use of chestnut leaves in traditional folk remedies spurred the research, led by Cassandra Quave, an ethnobotanist at Emory University.
The chestnut leaf extract is rich in ursene and oleanene derivatives, and blocks Staphlococcus aureus virulence and pathogenesis with no detectable resistance.
“We’ve identified a family of compounds from this plant that have an interesting medicinal mechanism,” Quave says. “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 finding opens up possibilities for new ways to both treat and prevent infections of methicillin-resistant S. aureus, or MRSA, without fueling the growing problem of drug-resistant pathogens.
“We’ve demonstrated in the lab that our extract disarms even the hyper-virulent MRSA strains capable of causing serious infections in healthy athletes,” Quave says. “At the same time, the extract doesn’t disturb the normal, healthy bacteria on human skin. It’s all about restoring balance.”
For years, she and her colleagues have researched the traditional remedies of rural people in Southern Italy and other parts of the Mediterranean.
“I felt strongly that people who dismissed traditional healing plants as medicine because the plants don’t kill a pathogen were not asking the right questions,” she says. “What if these plants play some other role in fighting a disease?”
Treating Skin Infections
“Castanea sativa” by Jean-Pol Grandmost. CC BY 3.0
Hundreds of field interviews guided her to the European 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,” Quave says.
The work produced an extract of 94 chemicals, of which ursene and oleanene based compounds are the most active.
Tests showed that this extract inhibits the ability of staph bacteria to communicate with one another, a process known as quorum sensing. MRSA uses this quorum-sensing signaling system to manufacture toxins and ramp up its virulence.
“We were able to trace out the pathways in the lab, showing how our botanical extract blocks quorum sensing and turns off toxin production entirely,” Quave says. “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.”
A single dose of the extract, at 50 micrograms, cleared up MRSA skin lesions in lab mice, stopping tissue damage and red blood cell damage. The extract does not lose activity, or become resistant, even after two weeks of repeated exposure.
And tests on human skin cells in a lab dish showed that the botanical extract does not harm the skin cells, or the normal skin micro-flora.
“We now have a mixture that works,” Quave says. “Our goal is to further refine it into a simpler compound that would be eligible for FDA consideration as a therapeutic agent.”