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The Weed Whisperer

Never discount the power of plants, even those commonly considered weeds

By Carol Clark

Story Photo

Ethnobotanist Cassandra Quave uncovered a medicinal mechanism in berries from the Brazilian peppertree. The plant is valued by traditional healers in the Amazon as a treatment for infections. Photo by Ann Borden

weedThe red berries of the Brazilian peppertree—a weedy, invasive species common in Florida—contain an extract with the power to disarm dangerous antibiotic-resistant staph bacteria, found Emory ethnobotanist Cassandra Quave.

"Traditional healers in the Amazon have used the Brazilian peppertree for hundreds of years to treat infections of the skin and soft tissues,"  says Quave, an assistant professor in the Department of Dermatology. "We pulled apart the chemical ingredients of the berries and systematically tested them against disease-causing bacteria to uncover a medicinal mechanism of this plant."

In an article published in Scientific Reports (, Quave and her lab team showed that a refined, flavone-rich composition extracted from the berries inhibits formation of skin lesions in mice infected with methicillin-resistant Staphylococcus auereus (MRSA).

The compound works not by killing the MRSA bacteria but by repressing a gene that allows the bacteria cells to communicate with one another. Blocking that communication prevents the cells from taking collective action, a mechanism known as quorum quenching.

"It essentially disarms the MRSA bacteria, preventing them from excreting the toxins used as weapons to damage tissues," Quave says. "The body's normal immune system then stands a better chance of healing a wound."

The discovery may hold potential for new ways to treat and prevent antibiotic-resistant infections, a growing international problem. Antibiotic-resistant infections annually cause at least 2 million illnesses and 23,000 deaths in the United States, according to the CDC.

The United Nations last year called antibiotic-resistant infections a "fundamental threat" to global health and safety, citing estimates that they cause at least 700,000 deaths each year worldwide, with  the potential to grow to 10 million deaths annually by 2050.

Blasting deadly bacteria with drugs designed to kill them is helping to fuel the problem of antibiotic resistance. Some of the stronger bacteria may survive these drug onslaughts and proliferate, passing on their genes to offspring and leading to the evolution of deadly "super bugs."

In contrast, the Brazilian peppertree extract works by simply disrupting the signaling of MRSA bacteria without killing them. The researchers also found that the extract does not harm the skin tissues of mice, or the normal, healthy bacteria found on skin.

"In some cases, you need to go in heavily with antibiotics to treat a patient," Quave says. "But instead of always setting a bomb off to kill an infection, there are situations where using an anti-virulence method may be just as effective, while also helping to restore balance to the health of a patient. More research is needed to better understand how we can best leverage anti-virulence therapeutics to improve patient outcomes." Botanical Illustration by Tharanga Samarakoon, PhD, Emory University Herbarium.

Related Links

"Brazilian peppertree packs power to knock out antibiotic-resistant bacteria" (News Story, 2/10/2017)

Quave Research Group

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