IS26-Mediated Formation of a Hybrid Plasmid Carrying mcr-1.1

PURPOSE: The objective of this study was to elucidate the characteristics and mechanism of formation of the fusion plasmid pHNSHP24 carrying mcr-1.1. MATERIALS AND METHODS: mcr-1.1-bearing Escherichia coli SHP24 and the corresponding transconjugant were subjected to whole-genome sequencing (WGS) combining the Illumina and MinION platforms to obtain the complete sequences of the fusion plasmid and its original plasmids. RESULTS: Complete sequence analysis and S1 nuclease-pulsed field gel electrophoresis (S1-PFGE) results indicated that E. coli SHP24 carried four plasmids: mcr-1.1-harboring phage-like plasmid pHNSHP24-3, F53:A-:B- plasmid pHNSHP24-4, pHNSHP24-1, and pHNSHP24-2. However, the plasmid pHNSHP24 carrying mcr-1.1 presents in the transconjugant differed from the four plasmids in the donor strain SHP24. Further analysis showed that pHNSHP24 may be the fusion product of pHNSHP24-3 and pHNSHP24-4 and is formed through a replicative transposition mechanism mediated by IS26 in E. coli SHP24. CONCLUSION: This study is the first to report the fusion of an mcr-1.1-harboring phage-like pO111 plasmid and an F53:A-:B- plasmid mediated by IS26. Our findings revealed the role of phage-like and fusion plasmids in the dissemination of mcr-1.1.