CRISPR-Cas9-mediated IncF plasmid curing in extraintestinal pathogenic Escherichia coli

IncF plasmids are commonly found in extra-intestinal pathogenic Escherichia coli (ExPEC) strains, serving as reservoirs for antimicrobial resistance (AMR) genes and virulence factors, persistently coexisting with ExPEC lineages. Multidrug-resistant (MDR) high-risk ExPEC clones, particularly ST131, ST1193, and ST410, have acquired diverse IncF plasmids over time, containing various AMR determinants, contributing significantly to their global success. However, the broader roles of these IncF plasmids in the success of MDR ExPEC clones, beyond AMR, remain elusive. In this study, we employed a novel clustered regularly interspaced short palindromic repeats–CRISPR-associated protein-9 nuclease (CRISPR-Cas9)-mediated pCasCure plasmid-curing system to precisely remove specific IncF plasmids among ExPEC clones (ST1193, ST131, and ST410). Antibiotic-resistant parent strains reverted to antibiotic-susceptible states post-curing; however, IncF plasmid curing did not show significant impact on bacterial in vitro growth and had little impact on other in vitro phenotypes, including survival in water, dry environment and biofilm production. In addition, IncF plasmid curing did not affect the conjugation frequency of KPC-producing pKpQIL plasmid. This study represents a pivotal initial step in understanding the precise roles of IncF plasmids in the success of ExPEC. Future research will be crucial in investigating their influence on cell invasion and in vivo fitness, thereby providing a more comprehensive perspective on the functions of IncF plasmids in MDR ExPEC clones.