Antimicrobial Resistance Characteristics and Mechanism of Imipenem-resistant Pseudomonas aeruginosa

OBJECTIVE To investigate the antimicrobial resistance characteristics of Pseudomonas aeruginosa and the mechanisms of imipenem-resistance from producing carbapenemase,lacking outer membrane protein and active efflux pump system.METHODS Thirty four strains from patients from Jan to Dec 2005 were identified and drug susceptibility test was performed by BD Phoenix100 automatic microbial analysis system,cefoperazone/sulbactam detection was performed by K-B method.Carbapenemases,including IMP,VIM,GIM,SPM,GES,OXA and outer membrane protein oprD2 genes were detected by PCR method.Etest and carbonyl cyanide m-chlorophenylhydrazone(CCCP) were used to study the affection on the minimal inhibitory concentrations(MIC) of imipenem.RESULTS Imipenem-resistant P.aeruginosa was all susceptible to amikacin,near half(48-54%) was susceptible to piperacillin and pipercillin/tazobactam,respectively,only 3-29% were susceptible to the other cephalosporins,aztreonam and quinolones.There were 29% of P.aeruginosa susceptible to meropenem and all resistant to amoxicillin/clavulanate,chloramphenicol,tetracycline and trimethoprim/sulfamethoxazole.The positive rate of IMP and oprD2 genes were 17.6% and 2.9%,respectively,while VIM,GIM,SPM,OXA,and GES genes were not detected.MIC to imipenem affected by CCCP was 11.8% in tested P.aeruginosa.CONCLUSIONS The resistance of P.aeruginosa to imipenem is a serious issue.The resistant P.aeruginosa to imipenem may be due to production of IMP metallo-β-lactamases,active efflux pump system or the loss of outer membrane protein oprD2,but lacking of oprD2 gene is not the main reason.