Objective:To probe the relationship between active efflux pump MexAB-OprM in clinical isolated Pseudomonas aeruginosa strains and the carbopenem resistance,and study its molecular mechanism of drug resistance.Methods:Antimicrobial susceptibili of Pseudomonas aeruginosa clinical isolates were tested by Kirby-Bauer method against inipenem and meropenem.The strains were divided into Carbapenems-resistant group and Carbapenems-sensitive group according to carbopenems sensitivity.RT-PCR method was used to study the level of mRNA expression of oprM which was the structural gene in active efflux pump MexAB-OprM.PCR method was used to amplify the mexR gene of these two group strains,and analyze the PCR products with DNA sequencing.Results:The expression level of mRNA of oprM in the strains of the Carbapenems-resistant group was significantly higher than those in Carbapenems-sensitive group(P0.05).One strains had the amino acid substitu-tionin in MexR protein,Val(GTG)→Glu(GAG) at the position of amino acid 126.Two strains had the amino acid substitutionin of Arg(CGG)→Gln(CAG) at the position of amino acid 70.Conclusion:In The First Affiliated Hospital of Shanxi Medical University,active efflux pumps in clinical isolated Pseudomonas aeruginosa mediate the resistance to carbopenem.High level expression of MexAB-OprM is related to mexR gene mutation and other mutant type.

Objective To study the mechanism of the Carbapenems-tolerance in Pseudomona aeruginosa ( P.aeruginosa ). Method Thirty-one strains of P. aeruginosa isolated from November 2008 to April 2009 in our hospital were analyzed. According to the results of drug sensitivity test, the thirty-one strains of P. aeruginosa were divided into Carbapenems-tolerance group(21 strains) and Carbapenems-sensitive group( 10 strains). Meanwhile, a standard strain of P.aeruginosa ATCC 27853 was also studied and an imipenem-EDTA inhibition test was conducted to detect metallo-beta-lactamases. PCR method was used to detect theoprD2 gene in P. aeruginosa,so as to study the mechanism of the Carbapenemstolerance inP. aeruginosa. Result 7 of 21 strains of Carbapenems-tolerance P. aeruginosa produced metallo-beta-lactamases; 15 of 21 strains of Carbapenems-tolerance P. aeruginosa were shown to be oprD2 gene negative, while the other 6 were positive. In contrast,all of the 10 strains of the Carbapenems-sensitive P. aeruginosa were found to be oprD2 gene positive,and so was the standard strain ATCC 27853. The results of the Chi-square test revealed that the difference between the positive rates of the oprD2 gene in the Carbapenems-tolerance and sensitive P. aeruginosa was statistically highly significant.Conclusion Loss of the oprD2 gene and metallo-beta-lactamases-producing ability were the important mechnisms of the Carbapenems-tolerance in P. aeruginosa of our hospital.

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