Chimpanzees take their own antibiotics

Chemical analysis of several plants ingested only in specific instances show that they inhibit the development of pathogenic strains of bacteria such as ‘E. coli’

Chimpancés antibióticos
Chimpanzees eat at least a dozen plants for their medicinal, not nutritional, value. In the picture, one of the studied chimpanzees eats fruits of 'F. exasperate.'Elodie Freymann
Miguel Ángel Criado

A few weeks ago, it was learned that researchers had seen an orangutan applying a poultice with leaves from a medicinal plant to a serious wound on its face. Now, thousands of miles away, on another continent, it has been revealed that another great ape — the chimpanzee — uses a range of plants, from leaves to tree bark, to treat its ailments. The analysis of these plants, some commonly found in traditional medicine, has shown that most have antimicrobial properties, while a third have anti-inflammatory properties. The authors of the work believe that great apes may one day help humans discover new drugs.

The Budongo Forest Reserve in Uganda is home to several chimpanzee communities. Two of them — Sonso and Waibira — are used to the presence of scientists, who have been studying the two populations (the first made up of 68 chips and the second, 105) since the last century. Occasionally, they have been seen eating plants of unknown or no nutritional value. Suspecting their possible medicinal use, a group of researchers collected dozens of extracts from 17 part-specific samples across 13 different species (taking samples from dead wood, leaves and bark) that were not part of the chimps usual diet. In parallel, they analyzed stool and urine samples from both groups to detect diseases, with the team playing close attention to the behavior and health of 51 of the animals.

As detailed in the scientific journal PLoS ONE, the samples were analyzed at the Neubrandenburg University of Applied Sciences in Germany — in the laboratory led by Dr. Fabien Schultz, co-author of the study — to determine their anti-inflammatory and antibiotic properties. The researchers collected 53 extracts using different methods, and then analyzed their pharmacological effects.

“We tested these extracts for their antibacterial and anti-inflammatory effects,” says Schultz, an ethnopharmacologist who has spent years studying the connection between traditional medicine in human communities and the medicinal plants consumed by primates. “In our in vitro antibiotic trials, we investigated the effects of the extracts against the growth of 11 different strains of bacterial pathogens. These included clinical isolates of the so-called ESKAPE pathogens, which the WHO considers one of the greatest threats to global health,” he adds.

The researchers also tested against pathogenic strains of bacteria, such as Escherichia coli, and multiresistant ones, such as Staphylococcus aureus or Klebsiella pneumoniae. “All the strains used in our study had resistance to multiple drugs, often against the most important antibiotics that exist,” says Schultz. Nearly all of them had some kind of effect: 45 of the plant extracts (88%) showed at least some antibacterial activity at the lowest test concentration against at least one strain.

The researchers showed that plant extracts had antibacterial effects, but, as Schultz points out, this “does not tell us anything about the potency of these herbal remedies; simply that there are active ingredients that cause such effects.”

Potency was evaluated using dose-response experiments. In this way, the researchers identified the most powerful extracts, such as the one taken from dead wood of Alstonia boonei, a deciduous tree present in much of sub-Saharan Africa and used by many human communities as medicine. In the experiments, the extract worked best against S. aureus — a bacterium that’s of concern to hospitals — and Enterococcus faecium, which is commonly found in the human digestive system, but can become pathogenic, causing meningitis in newborns.

The researchers also found that the bark and resins of Khaya anthotheca, a large tree, had great resistance against both Enterococcus faecium and E. coli. In the last two years of monitoring, the researchers observed several chimpanzees with intestinal parasites eating the wood of Alstonia boonei and the bark and resin of Khaya anthotheca.

Before this study, it was known that several chimpanzee communities ingested leaves or other parts of plant species to combat intestinal parasitic infections. But for many of the leaves, their curative effect is mechanical in nature: they have no active ingredient. The chimps are unable to digest the leaves, which are covered with rough trichomes, they are able to take out intestinal worms such as nematodes when they leave the body. But the use of plants with antibiotic properties had not been documented in this detail. And it wasn’t just antibiotic properties that the researchers detected.

As Oxford University researcher and lead author of the study, Elodie Freymann, explains, “a chimpanzee with a damaged hand looked for leaves of a fern with strong anti-inflammatory properties; no other individuals around it ate ferns, and this had only been seen once before in 30 years of observation.” The fern was from the Christella parasitica species.

A third of the species analyzed by the researchers had some anti-inflammatory or analgesic effect. Although it is difficult to connect intentionality with action and result, for Freymann, “this provides evidence to suggest that the chimpanzee may have sought out the ferns for their anti-inflammatory properties.” The team is planning to do further study to confirm the hypothesis that, in at least in these communities, chimps look for certain plants and not others when they have a certain ailment.

The image is one of the rare occasions when chimpanzees have been photographed eating bark and resin from the 'Khaya anthotheca' tree. They contain active ingredients effective against several bacteria and protozoa, such as the cause of malaria.
The image is one of the rare occasions when chimpanzees have been photographed eating bark and resin from the 'Khaya anthotheca' tree. They contain active ingredients effective against several bacteria and protozoa, such as the cause of malaria.Elodie Freymann

“It is important for us to remember that wounds are not the only ailments that animals suffer from, and there will be internal diseases for which animals will need to self-medicate,” says the Oxford researcher. “This can be more difficult to study than wounds, because you can’t physically see what’s wrong with the animal you’re studying, so to do this you need to take a multidisciplinary approach, analyzing behavioral anecdotes alongside health data and pharmacological outcomes,” she adds.

“The natural world is full of medicines that we depend on, as are our non-human neighbors. If we want to keep these animals safe, we must protect their medicine cabinet,” she continues, connecting the story of Rakus the orangutan in Sumatra, Indonesia, to the chimps of Uganda.

This “medicine cabinet” should also be protected for selfish reasons. Schultz, who is now investigating the use of medicinal plants by mountain gorillas, points out that “finding a blockbuster drug from natural materials is often like finding the needle in the haystack; however, our work has contributed to early-stage drug discovery.”

Of course, there is still a long way to go; an extract can contain more than 1,000 different substances. “We don’t know [yet] which substances are present, whether they are new to science and how potent they are. There may also be synergistic effects, i.e. a combination of substances causes the effect, not a single one,” says Schultz.

What’s more, the researchers have only provided scientific evidence of the extracts’ efficacy in vitro and still has to isolate the active ingredient(s) and determine whether they could be used in animal trials. Schultz concludes: “there is a long way to go, but in theory, we humans can learn from our closest animal ancestors and, one day, human lives may be saved thanks to the knowledge of chimpanzees.”

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