Reduced Porin Expression with EnvZ-OmpR, PhoPQ, BaeSR Two-Component System Down-Regulation in Carbapenem Resistance of <i>Klebsiella Pneumoniae</i> Based on Proteomic Analysis

Carbapenem-resistant Klebsiella pneumoniae (CRKP) has proven to be an urgent threat to human health. In order to explore the potential mechanisms underlying carbapenem-resistance, proteomics (TMT/LC-MS/MS) and bioinformatics approaches were employed. Proteomic profiling of CRKP and susceptible KP (sKP) isolate revealed the involvement of outer membrane, beta-lactam resistance pathway and two-component systems (TCSs) in carbapenem resistance. 27 CRKP strains and 27 susceptible Klebsiella pneumoniae strains were isolated from inpatients at the Second Xiangya Hospital, China to verified the mechanisms. Modified carbapenem inactivation method (mCIM) and PCR of common carbapenem resistance genes confirmed that 77.8% (21/27) of CRKP isolates were carbapenemase-producing. Porin expressions determined by SDS-PAGE and mRNA levels of major porins (OmpK35 and OmpK36) showed porin reduction in CRKP isolates. RT-qPCR detection of two-component systems (envZ, ompR, phoP, phoQ, baeS and baeR) revealed down-regulation of EnvZ-OmpR, PhoPQ, BaeSR TCSs. Expression of the TCSs, except ompR, were closely correlated with OMPs with the R value >0.7. Together, this study reaffirmed the importance of β-lactam resistance pathway in CRKP based on proteomic analysis. OmpK35/36 porin reduction and the debatable downregulation of EnvZ-OmpR, PhoPQ and BaeSR TCSs were confirmed in carbapenem resistance in Klebsiella pneumoniae.