engleski

First Report of Molecular Characterisation of Carbapenem-Resistant Acinetobacter baumannii in Different Intensive Care Units in University Hospital Split, Croatia

Acinetobacter baumannii is an important cause of nosocomial infections such as pneumonia, septicaemia, urinary tract infections, and wound infections 1. It may become resistant to a wide range of antibiotics, thus complicating the treatment of nosocomial infections 1. The emergence of carbapenem resistance in Acinetobacter baumannii has become a global concern since these β -lactams are often the only effective treatment left against many multiresistant strains . According to a recent report, the overall resistance rate to imipenem in A. baumannii isolated from 17 representative laboratories in Croatia was 1 % (range 0%-8%) . However, molecular basis of carbapenem resistance was not investigated yet. We would like to report the molecular epidemiology of carbapenem resistant strains obtained from clinical samples of several patients hospitalised on different intensive care units inside University Hospital Split, Croatia. Eleven isolates of A. baumannii with an unusual resistance profile were isolated during 2003 and 2004, from patients hospitalised in three different intensive care units (two adults and one children ICU) on different locations inside UHS. Routine susceptibility testing was done by standard disc diffusion method according to the National Committee for Clinical Laboratory Standards guidelines. All collected isolates of A. baumannii displayed intermediate (MICs>8 mg/L) or resistant (MICs>16 mg/L) profile to imipenem and/or meropenem. Minimum inhibitory concentrations were also determined for ceftazidime, cefepime, ceftriaxone, amikacin, gentamicin, ciprofloxacin and piperacillin-tazobactam by broth microdilution method according to CLSI recommendation.. All isolates were multidrug-resistant exhibiting highly resistance to ceftazidime, cefepime, piperacillin/tazobactam, amikacin, gentamicin, netilmicin and ciprofloxacin. No resistance to ampicillin/sulbactam was observed which is not in use in our hospital. The isolates were genetically characterized with pulsed-field gel electrophoresis (PFGE). The preparation of genomic DNA of A. baumannii isolates was performed as previously described. Oxacillinases were detected by using a standard PCR technique with primers specific for blaOXA-23, blaOXA-40, blaOXA-58, and blaOXA-69 genes. Production of metallo-β -lactamases was screened by E test-MBL and PCR with primers specific for VIM and IMP β -lactamases. Β -lactamases were prepared from overnight broth cultures, released by sonication and cell debris was removed by centrifugation. PCRs were positive for the OXA-69 like enzyme in ten Acinetobacter strains belonging to unique PFGE profile characterised to pulsotype A, while strain characterised to pusotype B was the only strain isolated from children intensive care unit and carbapenemase gene was not found with tested primers. No significant hydrolysis of imipenem was detected. Acccording to the bibliographical data OXA-69 is a naturally occurring oxacillinase in A. baumannii and it does not confer on the producing isolates significant resistance to carbapenems, thus it can be concluded that resistance to imipenem and meropenem in our isolates is due to other mechanisms such as porin loss or efflux. Spread of the pulsotype A with OXA-69-type oxacillinases was due to clonal dissemination of multi-drug resistant A. baumannii between two different adult Intensive Care Units, probably by hospital staff during medical procedures. The infection control team of the hospital implemented restriction of carbapenem usage and strict antiseptic techniques, which included the rigorous use of alcohol-clorhexidine solutions before and between patient and equipment contact and before leaving the unit. To our knowledge, this is the first report on the molecular characterization carbapenem resistance in A. baumannii in Croatia. A similar finding underscores the progressive emergence of these determinants in different geographic areas. Consequently, incidence and spread of multidrug-resistant A. baumannii nosocomial infections suggest the necessity of a surveillance program and enforcing adequate control measures in different hospital settings

oxacillinases ; beta-lactamases ; Acinetobacter baumannii

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