Emergence of a Carbapenem-Resistant Klebsiella pneumoniae Isolate Co-harbouring Dual bla(NDM-6)-Carrying Plasmids in China

The widespread emergence of carbapenem-resistant Klebsiella pneumoniae (CRKP) with limited therapeutic options has become a global concern. In this study, a K. pneumoniae strain called KP2e was recovered from a human case of fatal septic shock in a Chinese hospital. Polymerase chain reaction and sequencing, antimicrobial susceptibility testing, conjugation experiments, S1 nuclease-pulsed field gel electrophoresis/southern blot, whole genome sequencing and comparative genomics were performed to investigate the phenotypic and molecular characteristics of this isolate. KP2e possessed the NDM-6-encoding gene and exhibited resistance to almost all beta-lactams except for monobactam. This strain belonged to sequence type 4024, the complete genome of which was composed of one chromosome and three plasmids. Furthermore, bla(NDM-6) coexisted on two self-transmissible plasmids, which were assigned to types IncFIB and IncN. A structure of IS26-composite transposon capturing an identical Tn125 remnant (Delta ISAba125-bla(NDM-6)-ble(MBL)-trpF-dsbC-cutA-groES-Delta groEL) was identified in the two plasmids, and this conserved bla(NDM)-surrounding genetic context was similar to that of few IncN plasmids found in other regions of China. Our research appears to be the first description of a clinical strain that emerged co-harbouring dual bla(NDM)-carrying plasmids, and the first report of NDM-6-positive CRKP in China. These findings demonstrated that IncN is a key medium in the evolution and expanding dissemination of bla(NDM) genes among various species, which indicates that close monitoring and rapid detection of bla(NDM)-harbouring plasmids is necessary.