The Contribution Of MexAB-OprM Active Efflux System In Multidrug Resistant Pseudomonas Aeruginosa And Mutation Of MexR

ObjectiveTo study the contribution of MexAB-OprM active efflux system in multidrug resistant pseudomonas aeruginosa and mutation of mexR.Materials and methodsIsolates120 clinically-isolated pseudomonas aeruginosa were collected from January 2006 to December 2007 in The First Affiliated Hospital of Anhui Medical University . They were identified by MicroScan WalkAWay-40 analysator .MethodsStandard agar dilution was used to determine the minimal inhibitory concentration (M IC) of 120 strains of Pseudomonas aeruginosa isolated clinically. The 26 strains of multidrug resistant pseudomonas aeruginosa and the 15 strains of susceptible susceptible pseudomonas aeruginosa were selected. Based on fluorescent SYBR GreenⅠmethodology, two cloning vectors pMD18-T-mexB and pMD18-T-16SrDNA were constructed as standard plasmids. The levels of mexB mRNA of 15 susceptible strains and 26 multidrug resistant strains were detected by Real-time fluorescent quantitative PCR, the 16SrDNA gene was also amplified as control. To observe the inhibition of efflux pump inhibitors (EPIs) MC-207,110 in the 26 strains of multidurg resistant pseudomonas aeruginosa . mexR was amplified with PCR and PCR products were analyzed with DNAResultThe drug-resistant rates of 26 strains of multidrug resistant pseudomonas aeruginosa against 14 kinds of antibiotics were 100%. The mexB mRNA were examinated in all strains . The levels of mexB mRNA in multidrug resistant strains (2.41±1.10) were signifficantly higher than that of standard susceptible strains (1.47±0.83) (P<0.01). The excretion of CIP can be inhibited by MC-207,110 in 20 strains (76.9%) of multidrug resistant pseudomonas aeruginosa . Among 20 strains showing excretion , 15 carried mutation in mexR . The point mutations were 336G-A,603G-A,660G-A,584C-G,653T-A , the two latters resulted in the substitution of amino acids , which were 103Ala—Gly , 126Val—Glu respectively . The insertion mutation (insertion of GGC between 470 and 474) resulted in insertion of Gly between 66 and 68 .ConclusionThe overexpression of MexAB-OprM active efflux system are associated with resistance of pseudomonas aeruginosa . The mutation of mexR gene may be one of the reasons for high level expression of MexAB-OprM .