Piggybacking on niche-adaptation reduces the cost of multidrug resistance plasmids

The persistence of plasmids in bacterial populations represents a puzzling evolutionary problem with serious clinical implications due to their role in the ongoing antibiotic resistance crisis. Recently, major advancements have been made towards resolving this “plasmid paradox” but mainly in a non-clinical context. Here we propose an additional explanation for the maintenance of multidrug resistance (MDR) plasmids in clinical Escherichia coli strains. After co-evolving two MDR plasmids encoding last resort carbapenem resistance with an extraintestinal pathogenic E. coli strain, we observed that chromosomal media adaptive mutations in the global regulatory systems CCR (Carbon Catabolite Repression) and ArcAB (Aerobic Respiration Control) pleiotropically mitigated the costs of both plasmids. Mechanistically, cost reductions were due to a net downregulation of plasmid gene expression. Our results suggest that global chromosomal transcriptional re-wiring during bacterial niche-adaptation may facilitate plasmid maintenance. ### Competing Interest Statement The authors have declared no competing interest.