engleski

Preliminary results of the multicentre study on carbapenem resistance of Acinetobacter baumannii in northern Croatia

Objectives: The aim of the study was to characterize the mechanisms of carbapenem resistance in A. baumannii isolates collected in the frames of a multicenter study and to study their molecular epidemiology. Material and Methods: In total 115 A. baumannii isolates were collected in 13 diagnostic laboratories located in Northern part of Croatia in 2009. Antibiotic susceptibilities were determined by broth microdilution method according to CLSI. E-test MBL strips were used for detection of metallo-b-lactamases (MBLs). PCR was used to detect the presence of oxacillinases (OXA-51, OXA-23, OXA-24 and OXA-58) and MBLs of VIM, IMP and SIM series. The genetic context of blaOXA-51 and blaOXA-58 genes was determined by PCR mapping with the primers for ISAbaI and IsabaIII combined with forward and reverse primers for blaOXA-51 and blaOXA-58. Genotyping of the isolates was performed by PFGE. Results: There were 97% of the strains resistant to piperacillin, 94% to ceftriaxone, cefotaxime and gentamicin, 91% to ciprofloxacin, 89% to ceftazidime, 68% to tobramycin, 60% to amikacin and 29% to ampicillin/sulbactam. No resistance to colistin was observed. Colistin was the most potent antibiotic with MIC90 of 2 mg/L. Twelve isolates were found to be resistant to both carbapenems. Nine of them were shown to possess blaOXA58-like gene and three blaOXA-40 like gene. The strains susceptible to carbapenems were positive only for naturally ocurring OXA-51 b-lactamase whereas eight isolates with intermediate susceptibility to one or both carbapenems were shown to possess ISAbaI insertion sequence upstream of blaOXA-51 gene. No MBLs were found. Only OXA-58 b-lactamase was inhibited by sodium chloride. Chromosomal AmpC b-lactamases did not affect the susceptibility to carbapenems. None of the isolates exhibited significant synergy between meropenem and CCCP, indicating that overexpression of proton-gradient depended efflux pumps did not contribute to the meropenem resistance. The strains producing only OXA-51 b-lactamase were found to belong to EU clone I whereas OXA-40 and OXA-58 producers were asigned to EU clone II. Three strains positive for blaOXA-40 like genes were clonally related. Conclusions: The emergence of carbapenem resistance in A. baumannii in Northern Croatia is associated with the production of acquired oxacillinases belonging to OXA-58 and OXA-40 like groups. Carbapenem resistant isolates producing acquired oxacillinases belonged to EU clone II.

Acinetobacter; karbapenem; mechanism; resistant; hospital; strains

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