Recombination of plasmids in a carbapenem-resistant NDM-5-producing clinical Escherichia coli isolate

To investigate the genetic features of five plasmids recovered from an NDM-5-producing clinical Escherichia coli strain, BJ114, and to characterize the plasmid recombination event that occurred during the conjugation process.

The genetic profiles of the five plasmids were determined by PCR, conjugation, S1-PFGE, Southern hybridization and WGS analysis. Plasmid sequences were analysed with various bioinformatic tools.

Complete sequences of five plasmids were obtained. Two small plasmids, pBJ114-141 and pBJ114-46, were speculated to have recombined into a large fusion plasmid, pBJ114T-190. When conjugated to other E. coli strains, some of the fusion plasmids were able to be resolved into the original two single plasmids. A non-conjugative plasmid, pBJ114-96, exhibited a high degree of sequence identity with the phage P7-like plasmid as well as an mcr-1-bearing plasmid. Another plasmid, pBJ114-78, was found to contain multidrug resistance genes and various mobile elements.

The fusion plasmid recoverable from the transconjugant was found to be generated as a result of a recombination event that occurred upon interaction between a blaNDM-5-carrying plasmid and another plasmid present in the parental strain. Such recombination events presumably play a potential role in the dissemination of the blaNDM genes among different plasmids and pathogenic bacterial strains.