Abstract: Objective To investigate the characteristics and carbapenem-resistant mechanisms of Pseudomonas aerugi nosa(P.aeruginosa).Methods Minmium inhibitory concentration(MIC) of imipenem and meropenemagainst 162 strains of P.aeruginosa isolated from hospital were detected with agar dilution method.All the strains were screened for the outer membrane protein gene OprD₂ and carbapenemase genes such as VIM,MIP,SPM,and KPC with PCR,and then conformed with direct sequencing to identify subtypes.Carbonyl cyanidem-chloropheny lhydrazone(CCCP) was used as efflux pump inhibitor to detect membrane efflux mechanism.Results Among 162 strains tested,imipenem and meropenem resistance rates were 37.0% and 30.9%,respectively.In 60 imipenem and/or meropenem-resistant strains,50 strains were resistant to both drugs and the other 10 strains were only resistant to imipenem.In the resistant group,18 strains had a OprD₂ gene deletion,while in 102 into lerant strains of imipenem or meropenem(the sensitive strains),20 strains had a OprD₂ gene deletion. Thirteen carbapenemase positive strains were detected in the resistant group,5 of which were producing VIM-type,and 8 producing IMP-type.VIM,MIP genes were not detected in the sensitive group,and nostra in was detected positive in SPM-1,KPC gene.4813% of the resistant strains were efflux phenotype test positive,19 and 24 of which took imipenem and meropenem as substrates.10.8% of the sensitive strains were positive in the efflux test.Conclusion The situation of carbapenem resistance of P.aeruginosa is serious.The carbapenem resistance of P.aeruginosa results from interaction of severalm echanisms such as outermembrane protein loss,carbapenemase producing and active efflux pumping.