Transposition of insertion sequence element from KPC plasmid enhances intracellular survival of Klebsiella pneumoniae.

Background: The convergence of plasmids encoding Klebsiella pneumoniae carbapenemase (KPC) and virulence determinants is increasingly reported in K. pneumoniae (Kpn). However, how KPC plasmids interfere with the virulence plasmid-mediated pathogen-host interactions, and the significance of this interference in the within-host adaption of hypervirulent carbapenem-resistant K. pneumoniae (Hv-CR-Kpn), remain unclear.

Methods: An Hv-CR-Kpn variant based on ST11 CR-Kpn was created to determine the impact of capsular polysaccharide (CPS) in Kpn intracellular proliferation. Whole genome sequencing was conducted to find the cause of CPS loss. The biological significance of spontaneous CPS loss in Hv-CR-Kpn was ascertained with cell lines and murine model.

Findings: The acquisition of virulence plasmid resulted in CPS hyperproduction of CR-Kpn, attenuating the bacterial adherence to eukaryotic cells and intracellular proliferation. Spontaneous CPS loss was observed in the Hv-CR-Kpn after phagocytosis by macrophage, as a result from insertion sequence (IS) element transposition from KPC plasmid to chromosomal CPS gene cluster. The loss of capsule hyperproduction enhanced both the in vitro intramacrophage proliferation and evasion of antibiotic killing in vivo of CR-Kpn. The IncF plasmids, the vector for multidrug resistance genes, were characterised as the main reservoir of IS elements in Kpn genomes.

Interpretation: Loss of CPS production enhances the Kpn intracellular proliferation, facilitating evasion of antimicrobial killing. In addition to encoding carbapenemase, IS element transposition acts as an auxiliary mechanism by which the KPC plasmid promotes the adaptive evolution of Hv-CR-Kpn, aiding bacterial survival within the host environment.

Funding: Noncommunicable Chronic Diseases-National Science and Technology Major Project of China, National Natural Science Foundation of China, Key Scientific Innovation Project of Shanghai Municipal Education Commission and Shanghai Sailing Program.