Tiny jumping genes fingered as culprit in rise of antibiotic
Biomedical engineers believe they have discovered the physical mechanism that causes high doses of antibiotics to promote the spread of antibiotic resistance between bacteria. The culprit, they say, is an overabundance of 'jumping genes,' called transposons, that carry the genetic instructions for resistance from the cell's source code to plasmids that shuttle between cells.

In a series of experiments, Yao exposed cells resistant to various types of antibiotics to a range of concentrations of that antibiotic. As the concentration increased, invariably there came a point at which the cells carrying plasmids with more copies of the resistance genes began outcompeting their peers.

The researchers say that the copy number of transposons on the plasmids affects how many antibiotic resistance proteins the cell is producing. That production comes at an energy cost, and it's not until the amount of antibiotics reaches a certain level that the extra energy expended is a valuable trait to carry.

Source: https://www.nature.com/articles/s41559-022-01705-2