LAUSR

OBJECTIVES Mobile colistin resistance genes (mcr) encoded on conjugative plasmids, although described only relatively recently, have been reported globally in both humans and livestock. The genes are often associated with ISApl1 which can transpose the genes to novel genetic locations. Since the first report, multiple variants of mcr have been discovered on a variety of genetic locations in Escherichia coli, in plasmids and integrated into the chromosome. METHODS Using hybrid assembly of short-read and long-read WGS data, the presence of mcr-1 was confirmed on an IncI1 plasmid in E. coli. In vitro conjugation assays were performed to determine the potential to transfer between strains. Genetic comparison to previously reported IncI1 plasmids was performed. RESULTS The genomic sequence has identified that mcr-1 is present on a complete IncI1 plasmid. Comparison to previously reported ESBL-encoding plasmids from E. coli in the Netherlands from the same time period indicated a distinct lineage for this plasmid. CONCLUSION The observation of mcr-1 on an IncI1 plasmid confirms that the genetic region of this gene is actively transposed between genetic locations. This active transposition has consequences for the study of the epidemiology of mcr in populations.