DNA analysis of wild brown bear teeth shows that the global health threat has spread to remote areas of Sweden
Antibiotic resistance is described as “one of the biggest threats to global health, food security and development today” by the World Health Organization. It has spread to humans around the globe—and even wildlife deep in the forest.
Scientists say this medical condition—which occurs when bacteria change in response to the medicines used to treat infections—is detectable among brown bears in Scandinavia. Researchers at Uppsala University in Sweden report that tooth plaque from bear skulls dating back nearly two centuries shows marked increases in antibiotic resistance over the past 70 years.
“This is bacteria that we brush off every morning and every evening when we clean our teeth, but bears don’t have oral hygiene,” team member Katerina Guschanski, a university geneticist, tells Charlotte Hartley of New Scientist.
Published in the peer-reviewed journal Current Biology, the study cites the results of DNA analysis of scrapings of teeth from bear skulls dating to 1842 at the Swedish National Museum. The scientists found that antibiotic resistance in the large mammals—many secluded far deep in the woods away from humans—spiked after the introduction of the class of drugs in Sweden in 1951.
“When humans start using antibiotics, antibiotics get into the environment,” Guschanski tells Andrew Curry of Science.
The study states that antibiotic-resistant bacteria are released from hospitals and people through wastewater treatment facilities and are dispersed through waterways. Animals in the wild can then acquire these microbes and pass them back to humans while they hike or hunt.
Jaelle Brealey, the study’s lead author and now a postdoctoral fellow at the Norwegian University of Science and Technology, says her team examined bacterial deposits taken from the skeletal remains of wild brown bears in the collection of the Swedish National Museum to see how they have changed. The researchers took samples from teeth dating from 1842 to 2016.
“We specifically looked for bacterial genes that provide resistance to antibiotics,” she tells Andrei Ionescu of Earth.com. “Their abundance closely follows human antibiotic use in Sweden, increasing in the 20th century and then decreasing in the last 20 years. We also find a greater diversity of antibiotic resistance genes in the recent past, likely as a result of different kinds of antibiotics being used by humans.”
Brealey and the other scientists conclude in their report that the spread of antimicrobial resistance (AMR) genes can be reversed if countries take the necessary steps to curb the overuse of antibiotics. Sweden, a leader in this effort, implemented a nationwide program to reduce antibiotic resistance in 1995. It was also one of the first countries to ban antibiotics in farm animals, reports Chris Dall of CIDRAP News, the communications arm of the Center for Infectious Disease Research and Policy at the University of Minnesota.
“Our case study suggests that human actions, both negative and positive, can directly impact diverse microbial communities, including those associated with wild animals, and provides evidence that large-scale policies limiting the use of antimicrobials in humans and livestock may be effective in curbing the dissemination of AMR through environmentally mediated pathways,” the study states.