engleski

Carbapenem resistance in Acinetobacter baumannii isolates from children

Carbapenems have a potent activity against Acinetobacter spp and are often used as last resort for the treatment of infections due to multiresis tant Acinetobacter baumannii isolates. However, Acinetobacters may develop resistance to carbapenems through various combined mechanisms including decreased permeability, altered penicillin binding proteins (PBPs) and, rarely, efflux pump overexpression. Nine Acinetobacter baumanii strains were isolated from children'specimens at intensive care units during last three months of 2009. at Clinical Hospital Center Zagreb. The aim of the study was to characterize carbapenem-resistance mechanisms in these isolates. Material and methods The antimicrobial susceptibility to a wide range of antibiotics was determined by broth microdilution method according to CLSI guidelines. Modified Hodge Test (MHT) was used to screen for production of carbapenemases. MBL E-test was used to screen for production of metallo-β-lactamases. Genes encoding oxacillinases and metallo-beta-lactamases were detected by multiplex PCR. Genotyping of the strains was performed by pulsed-field gel electrophoresis (PFGE), and determination of sequence groups by multiplex PCR. Three of nine strains were resistant to imipenem and meropenem. They were found to produce OXA-24 β-lactamase, belonged to sequence group 1 (EU clone II) (Fig. 1) and were not clonally related by PFGE (Fig. 2). Other six strains were susceptible or intermediate susceptible to carbapenems, but showed variable levels of susceptiblity/resistance to gentamicin, expanded-spectrum cephalosporins, piperacillin/tazobactam and ciprofloxacin (Table 1). Multiplex PCR revealed only the intrinsic, naturally occurring OXA-51 β-lactamase of species A. baumannii. These strains showed distinct PFGE profiles and were also not clonally related. No MBLs were found.. Conclusions The study demonstrated ocurrance of carbapenem resistant OXA-24 producing A. baumannii at paediatric units of University hospital center Zagreb. Infections with such multiresistant isolates are associated with increased mortality and morbidity of infected chlidren. This study highlights the need to establish an antimicrobial surveillance network for A. baumannii to monitor the trends and new types of resistance mechanisms at paediatric hospital units. Furthermore, the factors responsible for dissemination of such strains need to be identified, controlled and prevented to avoid major outbreaks. High resistance rates to ciprofloxacin are difficult to explain because fluoroquinolones are not prescribed in children.

Acinetobacter baumannii ; carbapenemases ; OXA-24 beta-lactamase

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