engleski

MOLECULAR CHARACTERIZATION OF CARBAPENEM RESISTANCE IN ACINETOBACTERI BAUMANNII ISOLATES FROM ZAGREB, CROATIA

Background and aim Recently an increasing trend of carbapenem resistance has been observed in Acinetobacter baumannii. Carbapenem resistance results from metallo-β-lactamases, carbapenem hidrolyzing oxacillinases, loss of outer membrane proteins, efflux and often combined mechanisms of resistance. The aim of the study was to characterize carbapenem hydrolyzing enzymes in A. baumannii strains from Zagreb, Croatia. Material and methods Thirty three carbapenem resistant Acinetobacter baumannii isolates were collected from various clinical specimens and hospital units during 2008 in Clinical Hospital Center Zagreb, Croatia. The susceptibility to a wide range of antibiotics was determined by broth microdilution method according to CLSI. Metallo-β-lactamases (MBL) were detected by E test and by PCR with primers specific for IMP and VIM MBLs. The presence of blaOXA genes was determined by PCR with primers specific for OXA-51, OXA-69, OXA-23, OXA-24 and OXA-58 β-lactamases. ISAbaI insertion sequence was determined by PCR as described previously. Results All strains were resistant to ceftazidime, cefotaxime, piperacillin/tazobactam and gentamicin. Isolates were intermediate or resistant to cefepime, imipenem and meropenem. 30% of the strains were resistant to ciprofloxacin. No resistance to colistin and ampicillin/sulbactam was noticed. The strains were negative for MBLs by E test. No blaVIM and blaIMP genes were detectd. PCR detected the presence of OXA-51/69 β-lactamase. OXA-23, OXA-24 and OXA-58 β-lactamases were not found. ISAbaI insertion sequence was found upstreams of blaOXA-51 gene in all tested strains. Conclusions This study found the presence of OXA-51/69 β-lactamase in all tested isolates which is a naturally occuring oxacillinases in A. baumannii found im most strains with a variable expression. However, the level of carbapenem resistance depends on the amount of β-lactamase. The presence of ISAbaI insertion sequence upstreams of the blaOXA-51 gene in our isolates most likely increased the expression of the gene and was associated with carbapenem resistance. Our isolates were multidrug resistant and pose serious therapeutic problem in the hospital. Colistin and ampicillin/sulbactam are in most cases the only therapeutic option. Molecular typing of the strains by pulsed-field gel electrophoresis needs to be done to determine if the strains are clonally related.

cinetobacter baumannii; carbapenems; oxacillinases

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