Loss of mcr Genes Mediated by Plasmid Elimination and ISApl1.

We characterized the stability of a plasmid pCP53-mcr1_3 encoding mcr-1 and mcr-3.19 with and without colistin exposure during cultural passages via S1-pulsed-field gel electrophoresis (PFGE) and nanopore MinION sequencing. Both mcr-1 and mcr-3.19 were missing in certain subclones, mediated by genetic excision (ISApl1-mcr-1-pap2), and deletions of large multidrug resistance (MDR) regions confirmed by ISApl1 and plasmid elimination. Without colistin exposure, the eradication of mcr genes is feasible, while the factors influencing the elimination processes warrant further study.