| ObjectiveThe resistance and homology of imipenem-resistant Pseudomonas aeruginosa were studied to establish bases for clinical usage of antimicrobial agents reasonably,the development and study of new drugs ,and reforcing infection controls and monitoring the variance of resistant strains by describing the antimicrobial resistance, and investigating the mechanism of imipenem resistance and typing of metallo-β-lactamases.Methods29 strains of imipenem-resistant Pseudomonas aeruginosa were collected from Tongji hospital between January and September ,2004. Agar dilution method was made to determine the minimal inhibitory concentrations(MICs) of various antimicrobial agents according to the approved standard of CLSI.The metallo-β-lactamases- producing strains were screened by the double-disk synergy test and the metallo-β-lactamase gene was detected by polymerase chain reaction and sequencing methods.The activity of metallo-β-lactamase was determined spectrophotometrically.All of 29 strains of Imipenem-resistant Pseudomonas aeruginosa were typed by pulsed field gel electrophoresis(PFGE).ResultsThe trend of the resistance of Pseudomonas aeuginosa to imipenem has been increasing from 7.3% in 1998 to 14.3% in 2004.The resistance of 193 strains of Pseudomonas aeuginosa isolated from Tongji Hospital from January to September ,2004 to cefotaxime, gentamycin and tetracycline was 38.5%,42% and 93.7%.The resistance of Pseudomonas aeuginosa to other antimicrobial agents studied was all below 20%.Imipenem and meropenem/ceftazidime interresistant Pseudomonas aeuginosa were 11.0%(15 strains) and 7.3%(14 strains).The resistance of imipenem-resistant Pseudomonas aeuginosa and imipenem-susceptible Pseudomonas aeuginosa to tetracycline was both above 90%, and to piperacillin/tazobactam was 28.6% and 17.9% respectively.The resistance of imipenem-resistant Pseudomonas aeuginosa to other antimicrobial agents studied was higher than that of imipenem-susceptible Pseudomonas aeuginosa and the significance between them was obvious(P<0.01).The antimicrobial agents susceptibility test showed that all of 29 strains of imipenem-resistant Pseudomonas survived were multidrug-resistant.The resistance of them to cefotaxime and ceftazidime was 69% and 27.6% respectively. The MIC50 and MIC90 of aztreonam and amikacin were both 16μg/ml and 256μg/ml ,with the resistance was both 44.8%.The resistance of imipenem and meropenem was 93.1% and 69% respectively, with the MIC50 and MIC90 were all 32μg/ml and 256μg/ml.The MIC of 34.5%(10/29) imipenem-resistant Pseudomonas was above 32μg/ml,which belonged to the high-level resistance.The resistance of gentamycin and amikacin was 82.8% and 44.8% respectively, with the MIC50 of them were 256μg/ml and 16μg/ml respectively, and the MIC90 were both 256μg/ml.The resistance of ciprofloxacin, piperacillin/tazobactam and tetracycline were 41.4% ,48.3% and 100% respectively.Using double-disk synergy testing to detect the metallo-β-lactamase could find that the positive rate of 29 strains of Pseudomonas aeruginosa were 37.9%(11/29).But polymerase chain reaction detected only two strains of Pseudomonas aeruginosa producing metallo-β-lactamase.The enzyme activity of two strains of metallo-β-lactamase-producing Pseudomonas aeruginosa were 27.35±3.25U , 26.58±3.18U respectively with UV spectrophotometry.29 strains were classified into 16 types based on PFGE pattern. Type A,B,C,D,E,F,G contained two strains of imipenem-resistant Pseudomonas respectively.Type D contained 3 strains of imipenem-resistant Pseudomonas isolated from different patients of transplant surgery(2) and neurology ward(1).The time of collection of 3 strains was very close and all of 3 patients used respirometer.Other type contained one strain of imipenem-resistant Pseudomonas respectively.Two strains of metallo-β-lactamase producers belonged to different type.ConclusionThe resitance of Psedomonas aeruginosa isolated from Tongji Hospital from Januray to September,2004 to cefotaxime,gentamycin and tetracycline was 38.5%,42% and 93.7% respectively, The resistance of Pseudomonas aeuginosa to other antimicrobial agents studied was all below 20%.The resistance of imipenem-resistant Pseudomonas aeuginosa to antimicrobial agents was higher than that of imipenem-susceptible Pseudomonas aeuginosa, and the significance between them was obvious(P<0.01) other than tetracycline and piperacillin/tazobactam.Imipenem-resistant Pseudomonas aeuginosa was often mutidrug-resistant.The resistance of 29 strains of Imipenem-resistant Pseudomonas aeuginosa to cefotaxime,genmycin,meropenem and tetracycline was above 60%,to ciprofloxacin, aztreonam ,amikacin and piperacillin/tazobactam was 41～48% and to ceftazidime was 27.6%.The positive rate of metallo-β-lactamase-producing Pseudomonas aeuginosa was 37.9% by double-disk synergy testing.But using polymerase chain reaction found that two strains of Pseudomonas aeruginosa produced metallo-β-lactamase.The PFGE pattern indicated that small range epidemic existed in Tongji hospital which was the clone transmission of imipenem-resistant Pseudomonas aeuginosa.The horizontal transmision of enzyme genes has not been found among imipenem-resistant Pseudomonas aeuginosa.
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