Contribution of active efflux systems MexAB-OprM and MexXY-OprM to the antibiotic resistance of Pseudomonas aeruginosa

Objective To investigate the role of active efflux systems MexAB-OprM and MexXY-OprM in the multidrug resistance of Pseudomonas aeruginosa.Methods Thirty-six strains of multidrug-resistant P.aeruginosa were isolated from clinical specimens.The minimum inhibitory concentration(MIC) to cefotaxime was determined by agar dilution technique.The interference experiment was conducted in the presence of pump inhibitor carbonyl cyanide m-chlorophenylhydrazone(CCCP).The mRNA of mexA and mexX gene was analyzed by real-time RT-PCR to estimate the expression level of MexAB-OprM and MexXY-OprM efflux systems.The amplified products were analyzed by sequencing.The mechanism of overexpression was studied using Blast software.Results In the presence of CCCP,24 of the 36 strains of P.aeruginosa showed 4 times or higher increase of susceptibility to ciprofloxacin.The active efflux phenotype was identified in 66.7%(24/36) of the strains.MexAB-OprM efflux system was overexpressed in 41.7%(15/36) of the strains.MexXY-OprM efflux system was overexpressed in 58.3%(21/36) of the strains.Fifteen strains overexpressed both MexAB-OprM and MexXY-OprM efflux systems simultaneously.Mutation of mexR and mexZ with corresponding amino acid substitution was identified in 4 of the strains overexpressing mexA and mexX.Conclusions Overexpression of active efflux systems MexAB-OprM and MexXY-OprM in multidrug-resistant P.aeruginosa is one of the mechanisms contributing to the multidrug resistance of the bacteria which is caused by the mutation of the regulatory genes mexR and mexZ,respectively.