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Tapping into nature to fight superbugs

Enrique Gili
November 29, 2016

With drug-resistant strains of bacteria jeopardizing the lives of hundreds of thousands of people and few new treatments on the horizon, scientists are looking to nature for answers.

Healthy snacks
Image: Dr. Cassandra Quave

Scientists have called it a "fundamental threat" to human health, comparing it to terrorism and climate change. Rising resistance to antibiotics has vexed the medical community for decades. Now a growing number of infectious bacteria are becoming immune to all known drugs, prompting fears we are heading toward a post-antibiotic era. 

Health experts estimate drug-resistant strains of bacteria, such as methicillin-resistant staphylococcus aureus (MRSA), tuberculosis and E. coli, claim the lives of 700,000 people each year globally. According to a 2013 report published by the British government, if left unchecked that figure could rise to 10 million by 2050, costing the global economy up to 100 trillion dollars. The "superbugs," as they are known, could kill otherwise healthy people visiting hospitals for routine medical procedures or to give birth.

Over-prescription and use of antibiotics in farming are partly to blame. And the pharmaceutical industry has developed few new antibiotics in recent years. But in the search for new treatments, some researchers are turning to other branches of science, such as ethnobotany, which combines the study of indigenous cultures with the study of plants to find answers in traditional medicine.

Traditional knowledge + science = ethnobotany

Cassandra Quave is one of the scientists looking to nature for answers. For her, the quest is personal. At the age of three she had a life-threatening staph infection following the loss of her leg. The loss, however, did not dampen her enthusiasm for the wild lands of central Florida, where she grew up. An abiding interest in the natural world and healing led her to grad school.

Researcher Cassandra Quave poses for a photo in her lab
Cassandra Quave in her labImage: Marco Caputo

Now a trained medical ethnobotanist at Emory University in the U.S. state of Georgia, Quave is a plant detective at heart. She takes painstaking notes on folk remedies and collects samples, uniting her interest in traditional knowledge with scientific inquiry to unlock the secrets of plants. Over the course of her career, she's gathered hundreds of species of plants that might lead to new drug discoveries. "My PhD was focused on documenting the traditional uses of wild plants for the management of skin disease," she said. 

Quave conducts much of her field research in isolated corners of Southern Europe, recording accounts of folk healers living in Italy, Sicily and Albania. "I like going to more isolated places because people engage with nature for their own survival," she said. It was traditional knowledge of medicinal plants in the Italian countryside that led Quave to the sweet chestnut tree, Castanea sativa, and its potential to fight MRSA. 

Tree of life

Quave's initial research into the tree was published in 2015 in the peer-reviewed journal PLOS One. She found extracts derived from the leaves could potentially lead to a drug compound able to block the spread of MRSA, a disease that can lead to a broad array of medical complications, ranging from mild rash to death. Rather than killing staph outright, the extract shuts down its ability to create toxins that cause tissue damage. 

"It's like taking the teeth out of a dog's bite. The idea is to reduce or to remove the toxicity of these infections," Quave told DW. Now her team is conducting additional research to test the efficacy of the compound. The results will be published pending peer review.

Photo of a sweet chestnut. Source: Picture-Alliance / dpa
The sweet chestnut tastes great but it's the compounds in the tree's leaves that the researchers are afterImage: picture-alliance/dpa

Castanea sativa is a broad-leaved chestnut tree with a European history dating back 2,000 years to the Roman Empire. Once prized by farmers and arborists throughout Europe and the United States for its shade and the nutritional value of its nuts, which are now consumed as a seasonal delicacy. Villagers have also long used the leaves to make a topical rinse to alleviate skin ailments, Quave said.

Nature's sorcerers

While some folk remedies have no scientific basis, ethnobotany has a few advantages when it comes to identifying plants with therapeutic value. First, it provides a quick field guide to plants useful for treating illness and disease. After all, humans have consumed potent plants for a variety of medical and spiritual reasons since time immemorial. Through trial and error, traditional healers have honed the use of these plants. "I think there's a lot to uncover and to understand from what would otherwise be considered folklore," Quave said.

Secondly, ethnobotany builds upon millions of years of evolution. Plants are nature's sorcerers. Since they can't fight or flee predators, or wander off in search of mates, they produce a brew of chemical compounds designed to fend off pests and attract pollinators. When humans consume these plants, the body may react in several ways. The chemical cocktails they contain may prove benign, poisonous, hallucinogenic - or even therapeutic.

Plants are laid out to dry on the ground outside
Quave collects plant samples in the remote countryside in search of new medicinal compoundsImage: Dr. Cassandra Quave

"The whole concept of natural products research is to take advantage of the defense molecules that plants, fungi and bacteria are making to protect themselves, to protect us," said Nadja Cech, a chemistry professor at the University of North Carolina in the US. 

Despite the advances in modern medicine and research that led to the rise of synthetic drugs, the use of plants for medical purposes remains prevalent worldwide. According to the World Health Organization, 80 percent of Africa's population relies on traditional medicine for their primary health care. In China, traditional herbal medicine accounts for 30 to 50 percent of total medical consumption. 

And if Quave's findings on chestnut leaves make the leap from the Italian countryside to the hospital, it would not be unprecedented. Approximately 74 percent of drugs based on plant compounds are the result of pursuing ethnobotanical leads. Quinine, aspirin and the cancer drug Taxol are just a few of the commonly used medications derived from plants. 

"There's a lot of excitement in this field right now because people realize that there is great potential for natural products for drug discovery," said Cech. "We haven't fully tapped into that."