CRISPR/Cas9-mediated carbapenemase genes and plasmids curing in carbapenem-resistant Enterobacteriaceae.

Combating plasmid-mediated carbapenem resistance is essential to control and prevent the dissemination of carbapenem-resistant Enterobacteriaceae (CRE). Here we conducted a proof-of-concept study to demonstrate CRISPR/Cas9-mediated resistance gene and plasmid curing can effectively re-sensitize CRE to carbapenems. A novel CRISPR/Cas9-mediated plasmid-curing system (pCasCure) was developed and electrotransferred into various clinical CRE isolates. The results showed that pCasCure can effectively cure blaKPC, blaNDM and blaOXA-48 in various Enterobacteriaceae species of Klebsiella pneumoniae, Escherichia coli, Enterobacter hormaechei, E. xiangfangensis and Serratia marcescens clinical isolates, with > 94% curing efficiency. In addition, we also demonstrated that pCasCure can efficiently eliminate several epidemic carbapenem-resistant plasmids, including the blaKPC-harboring IncFIIK-pKpQIL and IncN pKp58_N, blaOXA-48-harboring pOXA-48-like, blaNDM-harboring IncX3 plasmids, by targeting their replication and partitioning (parA in pKpQIL) genes. However, curing blaOXA-48 gene failed to eliminate its corresponding pOXA-48-like plasmid in a clinical K. pneumoniae isolate 49210, while further next generation sequencing revealed that it was due to IS1R mediated recombination outside the CRISPR/Cas9 cleavage site, resulting in blaOXA-48 truncation and therefor escaped plasmid curing. Nevertheless, the curing of carbapenemase genes or plasmids, including the truncation of blaOXA-48 in 49210, successfully restore their susceptibility to carbapenems, with > 8-fold reduction of minimum inhibitory concentration (MIC) values in all tested isolates. Taken together, our study confirmed the concept of using CRISPR/Cas9-mediated carbapenemase genes and plasmids curing to re-sensitize CRE to carbapenems. Further work is needed to integrate pCasCure in an optimal delivery system to make it applicable for clinical intervention.