Overview

• Published on September 25 in Science, the analysis concludes that a minority of plasmids accounts for most multidrug resistance worldwide.
• The team examined more than 40,000 plasmids from bacterial samples collected across six continents, leveraging archives with strains preserved since 1917.
• Ancestral plasmids initially lacked antimicrobial-resistance genes but gained them as antibiotic use expanded, with descendants now resistant to first-line and last-resort drugs.
• A three-pathway model is proposed, with MDR plasmids arising chiefly via resistance gene insertion or plasmid–plasmid fusion, and fusion variants showing high cross-species transfer.
• The authors say pinpointing dominant plasmid types can strengthen surveillance and could inform future plasmid-targeted therapies and predictive public-health models.