Overview

• Researchers analyzed more than 40,000 plasmids from bacterial samples across six continents, creating the largest dataset of its kind.
• Historical archives reaching back to 1917 enabled reconstruction of pre-antibiotic plasmids, which initially lacked resistance genes.
• The team formalized three evolutionary pathways, with modern multidrug resistance emerging through AMR gene insertion or plasmid–plasmid fusion.
• Fusion-derived plasmids are highly transferable between species, accelerating resistance to both first-line and last-resort antibiotics.
• The findings were published September 25 in Science, and authors say plasmid-targeted approaches are promising but still in early development.