SCIENTIFIC EDUCATIONAL CENTER science idea

For the first time in history, researchers from the University of Pittsburgh School of Medicine have discovered that bacteriophages (or simply phages) – tiny viruses that attack bacteria – are the key to starting a rapid bacterial evolution leading to the emergence of treatment-resistant "superbugs".

The researchers showed that, contrary to the dominant theory in the field of evolutionary microbiology, the process of adaptation and diversification in bacterial colonies does not begin with a homogeneous clonal population. They were surprised to find that most of the early adaptation was not caused by random point mutations. Instead, the scientists found that phages, which we usually think of as bacterial parasites – were what gave the winning strain an evolutionary advantage at an early stage.

"In fact, the parasite has become a weapon," the scientists say. "The phages gave the winners the means to win. What killed the more sensitive bacteria gave an advantage to others."

When it comes to bacteria, an attentive observer can trace their evolution for several days. Because of how fast the bacteria grow, it only takes a few days for bacterial strains to acquire new traits or develop antimicrobial resistance.

A new study shows that the evolution of bacteria and phages often goes hand in hand, especially in the early stages of bacterial infection. This is a multi-layered process in which phages and bacteria unite in a chaotic dance, constantly interacting and evolving together.

When scientists tracked changes in the genetic sequences of six bacterial strains of skin wound infection in pigs, they found that phage jumps from one bacterial host to another were rampant – even clones that did not receive an evolutionary advantage had phages included in their genomes.

Most clones had more than one phage integrated into their genetic material – often there were two, three or even four phages in one bacterium.

"This showed us how closely phages interact with each other and with new hosts," the scientists say. "Characterizing the diversity of early bacterial infections may allow us to reconstruct the history and trace complex evolutionary paths for clinical benefits."

The results were published in Science Advances.

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