Grows. 25 (UPI) – The increased use of antibiotics in medicine and agriculture from the 1950s to 1990s resulted in an increase in resistance to the drugs in wild Swedish brown bears, according to a study published Wednesday by Current Biology.
However, there has been a downward trend in antibiotic resistance after national guidelines were implemented to restrict use of the drugs, the researchers said.
“We found similar levels of antibiotic resistance in bears from remote areas and near human life,” said Katerina Guschanski, co-author of the study, in a press release.
“This suggests that the contamination of the environment with resistant bacteria and antibiotics is really widespread,” said Guschanski, researcher in ecology and genetics at Uppsala University in Sweden and the University of Edinburgh in Scotland.
Pathogens resistant to currently available antibiotics pose a significant global health threat.
Hundreds of thousands of people die each year from infections caused by resistant bacteria, including about 35,000 in the United States alone, according to the Centers for Disease Control and Prevention.
Resistant bacteria can get into the environment through sewage treatment plants in hospitals and other facilities and spread over great distances through water and wind, according to the research.
From there, they can be ingested by wild animals, which in turn can transmit resistant bacteria to humans during leisure activities or hunting, according to Guschanski and his colleagues.
Sweden was one of the first countries to introduce strict control measures on the use of antibiotics, banning antibiotics in agriculture in the mid-1980s and introducing a national strategy program against antibiotic resistance in medicine in 1995.
For this study, the researchers used historical specimens of bacterial communities that live in the mouths of wild animals and remain as solid tartar deposits – calcified dental plagues – on teeth from museum collections, to investigate the effects of man-made antibiotics over the entire history of their application.
They specifically focused on the bacterial microbiomes, or bacterial communities, of Swedish brown bears, up to 180 years old.
Scandinavian brown bears typically live far from humans, but sometimes get closer to villages and towns, the researchers said.
They expected to find more antibiotic resistance genes in bears that lived in more densely populated areas of Sweden, although they didn’t, they said.
However, oral bacteria from bears born after 1995 show low levels of antibiotic resistance, although not as low as those found in bears that lived before humans began mass production of antibiotics.
The results suggest that historical microbiomes, such as those used in this research, could be a tool to study environmental changes in response to new strategies to reduce contamination and pollution, the researchers said.
The study also shows how government measures can be effective at the national level to contain a major health threat, they said.
The abundance of “bacterial genes that confer resistance to antibiotics … closely follows the use of antibiotics in humans in Sweden.
“We have also seen a greater variety of antibiotic resistance genes in the recent past, probably as a result of the different antibiotics that are used by humans,” said Brealey, a postdoctoral fellow at NTNU in Norway.