[Genomic characteristics and mechanisms of horizontal plasmid transfer in

A retrospective analysis was conducted on a clinically isolated Klebsiella pneumoniae strain KP1050 that produces both New Delhi Metallo-β-lactamase (NDM)-1 and Imipenem-hydrolyzing β-lactamase (IMP)-4 carbapenemases. The minimum inhibitory concentrations of various antimicrobial agents were determined using the microbroth dilution method. Whole-genome sequencing was performed to identify the resistance genes and resistance plasmids carried by the strain. Conjugation assays and gene knockout techniques were employed to clarify the mechanisms of horizontal transfer of resistance plasmids. Klebsiella pneumoniae KP1050 was resistant to multiple antimicrobial agents, including carbapenems, and only susceptible to amikacin, tigecycline, and polymyxin. The strain belonged to ST1245, carrying the blaNDM-1 and blaIMP-4 carbapenemase resistance genes on the 59 730 bp IncN-type and 289 270 bp IncHI5-type plasmids, respectively. Both IncN and IncHI5-type plasmids harbored complete gene clusters encoding the type Ⅳ secretion system and could be conjugated to recipient bacteria; however, the conjugation efficiency of the IncN-type NDM-1 plasmid (1×10⁻³) was higher than that of the IncHI5-type IMP-4 plasmid (5×10⁻⁶). Knockout of key genes in the plasmid type Ⅳ secretion system revealed that the IncHI5-type IMP-4 plasmid was not an independently conjugative plasmid but could undergo horizontal transmission through conjugation with the assistance of the IncN-type NDM-1 plasmid. Interactions between plasmids can promote the spread of carbapenemase resistance genes.