[Mechanism of carbapenems resistance in Acinetobacter baumannii].
OBJECTIVE
To investigate the mechanism of carbapenems resistance in Acinetobacter baumannii.


METHODS
WHONET-5 software was used to analyze the trend of carbapenem resistance in Acinetobacter baumannii collected from 1999 to 2001 at Peking Union Medical College Hospital. Analytical isoelectric focusing was used to measure the pI of the beta-lactamase. Conjugation experiment was used to study the transfer of carbapenem resistance and plasmid DNA was extracted and purified with Qiagen Plasmid Mini Kit. The homology of the isolates was determined by pulsed field gel electrophoresis (PFGE). Integrase genes and blaIMP-, blaVIM-, blaOXA- genes for resistant isolates were amplified and sequenced.


RESULTS
Imipenem resistance in A. baumannii was ranged from 1.8%-8.5%, but only 9 resistant isolates were viable. They were co-resistant to other carbapenems, ceftazidime, aztreonam, and gentamicin, and four isolates were resistant to ciprofloxacin. Impipenem resistance could not be transferred to susceptible strains. No plasmid was extracted. Each isolate produced TEM-1, AmpC, and two enzymes (pI 6.7, 6.0), which can not be inhibited by cloxacillin and clavulanic acid. Each isolate had class I intergase gene. Nine isolates were all negative for PCR of blaIMP- and blaVIM- genes, but positive for blaOXA-23 specific PCR. Sequencing found 100% homology with blaOXA-23. PFGE found 3 clones (A type: 5 isolates; B type: 3 isolates; C type: 1 isolate). Control isolates (imipenem-susceptible, but ceftazidime, ciprofloxacin, and gentamicin resistant) were also A clone.


CONCLUSIONS
Production of OXA-23 carbapenemase in A. baumannii was one of the main mechanisms of carbapenems resistance at our hospital. It brings concern that imipenem-resistant clone has evoluted from nosocomial multiple-resistant strains.
Wang
Hui
H
Department of Clinical Laboratory, PUMC Hospital, CAMS and PUMC, Beijing, 100730, China. wanghuibj@hotmail.com
Liu
Ying-mei
YM
Chen
Min-jun
MJ
Sun
Hong-li
HL
Xie
Xiu-li
XL
Xu
Ying-chun
YC
D040981:Acinetobacter baumannii / Q000187:drug effects* / Q000235:genetics; D001426:Bacterial Proteins / Q000378:metabolism*; D015780:Carbapenems / Q000494:pharmacology*; D002442:Ceftazidime / Q000494:pharmacology; D018550:Cephalosporin Resistance; D004352:Drug Resistance, Microbial; D024901:Drug Resistance, Multiple, Bacterial; D016521:Electrophoresis, Gel, Pulsed-Field; D006801:Humans; D008826:Microbial Sensitivity Tests; D017422:Sequence Analysis, DNA; D001618:beta-Lactamases / Q000378:metabolism*
D001426:Bacterial Proteins; D015780:Carbapenems; D002442:Ceftazidime; D001618:beta-Lactamases; C063912:carbapenemase