Study on the multi-drug efflux pump of carbapenem-resistant Pseudomonas aeruginosa

Objective To study the multi-drug efflux pump of meropenem-resistant Pseudomonas aeruginosa.Methods The minimum inhibitory concentrations(MICs) of meropenem against 141 strains of P.aeruginosa were determined by agar dilution method with or without the presence of efflux pump inhibitor MC207110(20 mg/L).The expression level of efflux pumps mRNA were analyzed by real-time PCR.The coding genes and regulatory genes of efflux pumps were amplified and analyzed by PCR and DNA sequencing.Results The results of efflux pump phenotype testing showed that MIC values of meropenem decreased to 1/4 to 1/512 for 69.1% of the strains tested.The mRNA expression level of 4 efflux pump genes increased in 20 strains of meropenem-resistant P.aeruginosa,primarily MexEF-OprN(10 strains),followed by MexCD-oprJ(5),MexAB-OprM(4),and MexXY-OprM(3).The mRNA expression of both MexA and MexC genes increased in 2 of these strains.Sequencing results of the 4 efflux pump genes showed that MexAB-OprM overexpression was due to MexR mutation in 3 strains,and nalC mutation in 1 strain.nalD mutation was not identified.All the 5 strains with MexCD-OprJ overexpression showed nfxB mutation.All the 10 strains with MexEF-OprN overexpression had mexT mutation.All the 3 strains with MexXY-OprM overexpression showed mexZ gene mutation.The coding genes mexB,mexD,mexF,mexY of efflux pump did not mutate in the 20 strains.Conclusions Efflux pump may be one of the main mechanisms of P.aeruginosa resistance to meropenem.The overexpression of the efflux pump system is primarily due to the mutation of corresponding regulatory genes.