Antibiotics are medicines that fight bacterial infections that help save lives. However, there is a growing problem of antibiotic resistance. It happens when bacteria change and become able to resist the effects of an antibiotic. Each time you take antibiotics, sensitive bacteria are killed. However, resistant germs may be left to grow and multiply. Now, scientists in Gothenburg, Sweden, report they have traced back the evolutionary history of antibiotic resistance genes, by comparing bacterial genomes.

Their study, “A framework for identifying the recent origins of mobile antibiotic resistance genes,” was published in Communications Biology.

“Understanding from which bacterial taxa these genes were mobilized, and whether their origin taxa share common traits, is critical for predicting which environments and conditions contribute to the emergence of novel resistance genes,” the researchers wrote. This knowledge may prove valuable for limiting or delaying future transfer of novel resistance genes into pathogens. The literature on the origins of mobile resistance genes is scattered and based on evidence of variable quality. Here, we summarize, amend, and scrutinize the evidence for 37 proposed origins of mobile resistance genes.”

The researchers explored the claims of recent origins for antibiotic resistance genes, added information from public DNA-sequence-databases, and investigated the evidence at hand.

“Using state-of-the-art genomic analyses, we supplement and evaluate the evidence based on well-defined criteria,” noted the researchers. “Nineteen percent of reported origins did not fulfill the criteria to confidently assign the respective origin. Of the curated origin taxa, >90% have been associated with infection in humans or domestic animals, some taxa being the origin of several different resistance genes.”

“Given that the overwhelming majority of bacteria are harmless to us, it was quite surprising that these genes almost exclusively came from bacteria causing disease,” stated Joakim Larsson, professor, senior author of the study, and director of the Centre for Antibiotic Resistance Research at University of Gothenburg, CARe. “On the other hand, it makes some sense since such bacteria often trigger antibiotic use when we become infected, and other pathogens are often nearby, ready to engage in gene transfer. These findings underscore the microbial-rich gut flora humans and domestic animals given antibiotics as arenas for resistance evolution” he said.

The researchers concluded that the origin is still unknown for more than 95% of all known resistance genes.

“Most likely, most of them come from un-sequenced bacterial species. We know the majority of the species that frequently tend to reside in the gut or on the skin of ourselves and of domestic animals. Therefore, this points to an important role of a much less explored gene reservoir—the environmental microbiota. The role of the environment as a likely source for antibiotic resistance also stresses the need to reduce risks for resistance development in the environment, for example by limiting discharges of antibiotics through wastewaters,” said Larsson.

The researchers concluded that exploring the origins of antibiotic resistance genes can provide us with important insights to slow down the emergence of novel ARGs in the clinics.

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