By chance, the British doctor Alexander Fleming discovered in the 1920s penicillin, an antibiotic used to treat infections caused by sensitive bacteria. But its production did not become massive until the 1940s, when chemists Ernst Boris Chain and Howard Walter Florey they managed to synthesize it for commercial distribution. All three scientists won the Nobel Prize in Medicine or Physiology in 1945.
Although the use of these drugs allows treating bacterial infections, their repeated use in humans and domestic animals leads to the appearance of antimicrobial resistance, a new threat to public health that causes hundreds of thousands of deaths a year worldwide.
“Many countries have already implemented control measures to reduce the use of these compounds in medicine and agriculture – some of which serve to promote the growth of animals -“, he explains to SINC Katerina Guschanski, a researcher at the Center for Evolutionary Biology at the University of Uppsala in Sweden. In fact, this country was the first European state to completely ban antibiotics as growth promoters in 1986, reports the expert.
Since then, the Swedish government has established a program to control their use in the biomedical sector, so that their sale is reduced and these drugs are only used when absolutely necessary. “However, both Sweden and other countries in the world continue to use them to treat diseases. They have not stopped doing it ”, he regrets Guschanski.
Pollution that reaches brown bears
Without further action, antibiotics and resistant bacteria can be released. For example in hospitals, where they are administered to the environment through sewage treatment plants and spread through the water over great distances. From there they reach the wild animals, which in turn can transmit resistant bacteria to people during recreational activities or hunting.
Antibiotics reach wild animals, which in turn can transmit resistant bacteria to people during recreational activities or hunting.
Despite this, until recently the evolution of antibiotic resistance in wildlife since the beginning of mass production in the 1940s. Now, Guschanski’s team used specimens of wild brown bears, preserved in historical collections from around the world. Stockholm Natural History Museum in Sweden, to study its effects throughout the history of its application. The results are published in the journal Current Biology.
The researchers analyzed changes in bacterial communities – the microbiomes– that live in the mouth of these animals and that are preserved as solid calculus deposits in the teeth, which can remain unchanged for millennia. This allowed us to study what has happened to Swedish brown bears for 180 years.
“We extracted DNA of these samples and characterize the genes that transmit resistance to antibiotics. Bears are a good reflection of resistance in a larger environment, because they do not normally come close to human dwellings. Therefore, what we see in them is what happens in environments far from humans ”, the Swedish scientist emphasizes to SINC.
They found that the increased use of antibiotics in medicine and agriculture in the 1950s to 2000s led to increased resistance in wild Swedish brown bears. But they also detected a clear downward trend in said resistance after the application of national policies to control its use.
Increased use of antibiotics in medicine and agriculture in the 1950s to 2000s led to increased antibiotic resistance in wild Swedish brown bears
“We also see that the diversity of antimicrobial resistance genes in the oral bacteria of bears increases over time over the 180 years covered by our sample,” says the expert. In fact, in the newer samples, they detected a greater diversity of resistant genes than in the older samples, probably due to a greater diversity of types of antibiotics used by humans.
Further than previously thought
Scandinavian brown bears tend to live far away from humans, but occasionally they approach towns and cities. The researchers hoped to find more antibiotic resistance genes in bears that lived in more densely populated regions of Sweden. However, to his surprise, it was not.
“We found similar levels of antibiotic resistance in bears in remote areas and in those close to the human population. This suggests that contamination of the environment with resistant bacteria and antibiotics is really widespread, ”says Guschanski.
Now, the team intends to study the effects of antimicrobial resistance in other animals, such as foxes, badgers or deer, in the same way that they did with bears. “Species that are most closely related to the human population could be useful as sentinel species. They could serve as indicators of the immediate results of human action near homes ”, concludes the expert.