The key role of iroBCDN-lacking pLVPK-like plasmid in the evolution of the most prevalent hypervirulent carbapenem-resistant ST11-KL64 Klebsiella pneumoniae in China.

Aims: Hypervirulent carbapenem-resistant Klebsiella pneumoniae (hv-CRKP), coharboring hypervirulence and carbapenem-resistance genes mediated by plasmids, causes infections with extremely high mortality and seriously impacts public health. Exploring the transfer mechanisms of virulence/carbapenem-resistance plasmids, as well as the formation and evolution pathway of hv-CRKP is of great significance to the control of hv-CRKP infections.

Methods: In this study, we identified the predominant clone of hv-CRKP in China and elucidated its genomic characteristics and formation route based on 239 multicenter clinical K. pneumoniae isolates and 1014 GenBank genomes by using comparative genomic analysis. Further, we revealed the factors affecting the transfer of virulence plasmids, and explained the genetic foundation for the prevalence of Chinese predominant hv-CRKP clone.

Results: ST11-KL64 is the predominant clone of hv-CRKP in China and primarily evolved from ST11-KL64 CRKP by acquiring the pLVPK-like virulence plasmid from hvKP. Significantly, the virulence gene cluster iroBCDN was lost in the virulence plasmid of ST11-KL64 hv-CRKP but existed in that of hvKP. Moreover, the absence of iroBCDN didn't decrease the virulence of hv-CRKP, which was proved by bacterial test, cell-interaction test and mice infection model. On the contrary, loss of iroBCDN was observed to regulate virulence/carbapenem-resistance plasmid transfer and oxidative stress-related genes in strains and thus promoted the mobilization of nonconjugative virulence plasmid from hvKP into ST11-KL64 CRKP, forming hv-CRKP which finally had elevated antioxidant capacity and enhanced survival capacity in macrophages. The loss of iroBCDN increased the survival ability of hv-CRKP without decreasing its virulence, endowing it with an evolutionary advantage.

Conclusions: Our work provides new insights into the key role of iroBCDN loss in convergence of CRKP and hvKP, and the genetic and biological foundation for the widespread prevalence of ST11-KL64 hv-CRKP in China.