Oral bacteria from wild Swedish brown bears reveal history of antibiotic use in humans
An international team of researchers have used historical museum collections to study the effects of human-made antibiotics on the entire history of their application. They found that the increased use of antibiotics in medicine and agriculture in the 1950s-1990s led to an increase in antibiotic resistance in wild Swedish brown bears. However, they also detected a clear downward trend in antibiotic resistance after the implementation of national policies to control the use of antibiotics.
The study is published in the scientific journal Current Biology.
Antibiotic resistance is a major threat to global health, and hundreds of thousands of people die each year from infections with resistant bacteria. Antibiotics and resistant bacteria, for example from hospitals, can escape into the environment through wastewater treatment plants and spread by water and wind over great distances. From there, they can be picked up by wild animals, which in turn can transmit resistant bacteria to humans during recreational or hunting activities. However, studying how antibiotic resistance has changed in wildlife since the mass production of antibiotics began in the 1940s has not been possible until recently. Now scientists have used specimens from museum collections to analyze changes in bacterial communities that live in the mouths of wild animals and persist as solid tartar deposits on the teeth. This dental calculus can remain unchanged for millennia, which has enabled the study of historic bacterial communities, the microbiomes, of 180-year-old Swedish brown bears.
“We specifically looked for bacterial genes that offer resistance to antibiotics,” says Jaelle Brealey, postdoctoral researcher at NTNU in Norway and lead author of the study. “Their abundance closely follows human antibiotic use in Sweden, increasing in the 20th century and then decreasing over the past 20 years. We also find a greater diversity of antibiotic resistance genes in the recent past, probably due to different types of antibiotics used by humans. “
Scandinavian brown bears typically live far from humans but sometimes approach villages and towns. The researchers expected to find more antibiotic resistance genes in bears that lived in more densely populated areas of Sweden. However, to their surprise, no such relationship was observed.
We found similar levels of antibiotic resistance in bears in remote areas and those found near human dwellings. This suggests that contamination of the environment with resistant bacteria and antibiotics is really widespread. “
Katerina Guschanski, lead lead author of the study with joint appointments at Uppsala University and University of Edinburgh
Sweden was one of the first countries to implement strict control measures for the use of antibiotics, introducing a ban on antibiotics in agriculture in the mid-1980s and a national strategic program against antibiotic resistance. in medicine in 1995. These measures appear to have taken effect. Oral bacteria from bears born after 1995 exhibit low resistance to antibiotics, although not as low as in bears that lived before humans began mass production of antibiotics. Only a comparison of microbiomes over time could reveal these changes.
“Our study once again underscores the value of historical museum collections, such as that of the Swedish Museum of Natural History, as a unique resource for understanding the effect of recent human actions on the environment,” says Daniela Kalthoff, curator of the museum and a co-author of the study.
Historical microbiomes could be used not only to study the past, but also to monitor environmental changes in response to new strategies to reduce contamination and pollution. This study provides an encouraging example of how government policies can be effective in mitigating a major health threat at the national level. It shows that human actions, both negative and positive, have a profound effect on the environment.
Brealey, JC, et al. (2021) The oral microbiota of wild bears in Sweden reflects the history of human antibiotic use. Current biology. doi.org/10.1016/j.cub.2021.08.010.