IncX2 and IncX1-X2 hybrid plasmids coexisting in a FosA6-producing Escherichia coli strain

IncX plasmids are receiving much attention as vehicles of carbapenem and colistin resistance genes, such as bla_NDM, bla_KPC, and mcr-1. Among them, IncX2 subgroup plasmids remain rare. Here, we characterized IncX2 and IncX1-X2 hybrid plasmids coexisting in a FosA6-producing Escherichia coli strain that were possibly generated as a consequence of recombination events between an R6K-like IncX2 plasmid and a pLN126_33-like IncX1 plasmid. Variable multidrug resistance mosaic regions were observed in these plasmids, indicating their potential to serve as flexible carriers of resistance genes. The diversity of IncX group plasmid backbones and accessory genes and the evolution of hybrid IncX plasmids pose a challenge in detecting and classifying them.