In the wild depths of Sweden, the traces of an emerging global health threat to humans can be found. Scientists have discovered that the mouths of wild Swedish brown bears have been harboring antibiotic-resistant bacteria for decades, a sure sign of the overuse and abuse of antibiotics throughout the past century.
As reported in the journal Current Biology, this discovery did not come about by brave undergraduates swabbing the mouths of wandering bears. Instead, the team employed an interesting method of looking at the skulls of brown bears kept in historical museum collections.
Researchers managed to get a sharp insight into the bacterial communities that lived in the mouths of wild bears over the past two centuries by studying the preserved solid calculus deposits left behind on their teeth. From the calculus deposits, they were able to look around for evidence of antibiotic resistance genes that emerged in the bears’ microbiomes.
They found that the rise in antibiotic resistance in wild Swedish brown bears coincided with the start of antibiotic mass-production in the 1940s. There was then a significant decline in antibiotic resistance following restrictions on antibiotic use in agriculture implemented in the mid-1980s and a national strategic program against antibiotic resistance in medicine in 1995.
Since brown bears are a shy species and will typically try to avoid human settlements, it’s perhaps surprising that antibiotic-resistant bacteria — a hallmark of modern medicine and industrial agriculture — was so common in these wild animals. Unexpectedly, the researchers expected to see more evidence of antibiotic resistance genes in bears that lived closer to populated human settlements, but this wasn’t the case.
“We found similar levels of antibiotic resistance in bears from remote areas and those found near human habitation,” Katerina Guschanski, lead senior author of the study from Uppsala University in Sweden and the University of Edinburgh in Scotland, said in a statement.
Antimicrobial resistance is often said to be one of the greatest threats to society, human, and animal health, and economic prosperity. It occurs when microbial pathogens pick up chance mutations that endow them with invulnerability to antibiotics. Resistant bacteria are then able to survive antibiotic treatment and propagate by natural selection. This can occur naturally, but misuse of antibiotics in humans and animals is known to be accelerating the process.
Antibiotic resistance genes can also seep into natural ecosystems through horizontal gene transfer, whereby neighboring bacteria exchange their genetic materials with one another. Once again, considering brown bears typically avoid human activity, it’s worrying that these processes are still occurring in remote stretches of Sweden and it suggests that antimicrobial resistance is shockingly prevalent even in the natural world.
“This suggests that the contamination of the environment with resistant bacteria and antibiotics is really widespread,” commented Guschanski.