Study on efflux pump MexAB-OprM in carbapenem-resistant Pseudomonas aeruginosa

Objective To study the relationship between efflux pump MexAB-OprM and carbapenem resistance of Pseudomonas aerginosastrains.Methods The minimum inhibitory concentrations of imipenem and meropenem were determined by agar dilution method for 75 strains of P.aerginosain the absence or presence of MC207110 to screen the phenotypes of active efflux pump.Reverse transcriptase-polymerase chain reaction(RT-PCR)method was used to determine the mRNA expression level of mexA which encodes the membrane fusion protein in active efflux pump MexAB-OprM and the reference(housekeeping)gene rpoD.PCR method was used to amplify the regulatory genes mexR,nalC,and nalDof active efflux pump MexAB-OprM in the strains overexpressing the efflux pump.The PCR products were subject to DNA sequencing and BLAST analysis.Results Of the 75 P.aeruginosa strains,13(17.3%)were positive for efflux pump MexAB-OprM.Overexpression of the efflux pump was identified in10 of the 13 strains and associated with positive regulatory genes mexR,nalCand nalD.A Gly71→Glu mutation in nalC was found in9 strains,and a Ser209→Arg mutation in nalCwas identified in8 strains.Only one strain had a Thr158→Ile mutation in nalD.Eight strains had mutation in mexR.Conclusions Overexpression of multidrug efflux pump MexAB-OprM plays an important role in carbapenem resistance of P.aeruginosa.High level expression of MexAB-OprM is related to the mutations of its regulatory genes.