CpxR promotes the carbapenem antibiotic resistance of <i>Klebsiella pneumoniae</i> by directly regulating the expression and the dissemination of <i>bla</i>_KPC on the IncFII conjugative plasmid

<i>Klebsiella pneumoniae</i> is an important human pathogen known for its resistance to carbapenem antibiotics, especially the increasing carbapenem-resistant hypervirulent variants. The carbapenem resistance is mainly caused by the carbapenemase gene <i>bla</i>_KPC which was commonly found on the IncFII transferable plasmids in <i>K. pneumoniae</i> ST11 isolates in regions of China. However, the mechanisms of the plasmid-carrying <i>bla</i>_KPC regulation by the host strain are not clear. To investigate the chromosome-encoded two-component system (TCS) that regulates the carbapenem resistance of <i>K. pneumoniae</i> caused by <i>bla</i>_KPC, twenty-four TCSs of a carbapenem-resistant classical <i>K. pneumoniae</i> ST11 clinical isolate were knocked out. The deletion mutation of the TCS regulator <i>cpxR</i> exhibited increased sensitivity to carbapenem, which could be restored by complementation with <i>cpxR in trans</i>. Electrophoretic mobility shift, isothermal titration calorimetry and DNase I footprinting results revealed that CpxR directly bound to the promoter DNA of <i>bla</i>_KPC and the binding was abolished by disrupting the DNA-binding domain in CpxR. The subsequent <i>in vivo</i> assays using the <i>lacZ</i> reporter system and qPCR showed that CpxR upregulates the transcription of <i>bla</i>_KPC. Notably, CpxR was also found to activate the transfer of the <i>bla</i>_KPC-carrying IncFII plasmid between the hypervirulent <i>K. pneumoniae</i> and <i>E. coli</i> isolates, in which CpxR promoted the transcription of the <i>tra</i> operon via binding to its promoter region. These results provide an important insight into the regulation of the host factor CpxR in the plasmid-carrying carbapenemase gene in the classical and hypervirulent <i>K. pneumoniae</i>.