Pre- and postantibiotic epoch: The historical spread of antimicrobial resistance

A study tracing plasmids from 1917–1954 to today reveals over a century of evolution: while nearly all plasmids from the pre-antibiotic era lacked resistance genes and most never acquired them, a small subset evolved into the major drivers of global antimicrobial resistance in Gram-negative bacteria. Modern plasmids, shaped by complex microevolution and fusion events, have become highly recombinogenic, multi-replicon, self-transmissible elements that now represent the greatest risk for resistance dissemination and a serious threat to human health.