Resistance To Carbapenems And Ceftazidime And Detection Of Metallo-β-Lactamases Production And Encoded Genes In Clinical Isolates Of Acinetobacter Baumanii And Pseudomonas Aeruginosa

Objective: To investigate the resistance to carbapenems and ceftazidime in clinical isolates of Acinetobacter baumanii and Pseudomonas aeruginosa, to detect the metallo-β-lactamases production and encoded genes in imipenem-resistant and/or ceftazidime-high-resistant (MIC>128 g/ml) isolates. Methods: 101 Acinetobacter baumanii strains and 69 Acinetobacter baumanii strains plus 26 Pseudomonas aeruginosa strains that were resistant to imipenem and/or ceftazidime tested by MicroScan WalkAway-40 automatic system were isolate from clinical specimens in West China Hospital from April 2002 to January 2003 and from February 2003 to April 2003, respectively. The MICs of imipenem, meropenem and ceftazidime were determined by 2-fold agar dilution method followed by NCCLS recommendations. Metallo-p-lactamases production was detected by chelators-imipenem or -ceftazidime double disks test and chelators-imipenem and -ceftazidime agar dilution method. BlaIMP and blaVIM were amplified by PCR. Results: 56 Acinetobacter baumanii strains and 16 Pseudomonas aeruginosa strains were resistant to imipenem and/or high resistant to ceftazidime confirmed by agar dilution method. The majority of these strains were isolated from sputum. These strains distributed in 15 different clinical departments or wards in our hospital, however, more than a half were isolated from ICU. 11 Acinetobacter baumanii strains, none Pseudomonas aeruginosa strains and all 8 positive control strains from elsewhere were found to produce metallo-β-lactamase by chelators-imipenem and -ceftazidime agar dilution method. However, only 2 Acinetobacter baumanii strains and 2 positive control strains of total 8 were found to produce metallo-β-lactamaseby chelators-imipenem or -ceftazidime double disks test. None of the tested isolates from our hospital but all positive control strains have positive production by blaIMpand blaVIM PCR. Conclusion: Imipenem-resitant and/or ceftazidime-high-resistant Acinetobacter baumanii and Pseudomonas aeruginosa strains were found in our hospital and distributed widely. Only small proportion of Acinetobacter baumanii strains and none of Pseudomonas aeruginosa strains produce metallo- -lactamase. Probably, the metallo-p-lactamase produced by our Acinetobacter baumanii strains is neither IMP-1 like IMP enzymes nor VIM-2 like VIM enzymes, but is other types IMP or VIM enzymes or unknown one. Chelators-imipenem and -ceftazidime agar dilution method is better than chelators-imipenem or -ceftazidime double disks test for detection metallo-p-lactamase production.