Investigation of resistance genes by molecular methods in clinical isolates of Acinetobacter baumannii

Acinetobacter baumannii, which are usually resistant in a wide range of antimicrobial agents covering carbapenems, is an important causative agent of nosocomial infections. Carbapenems are accepted an important option for the treatment of Acinetobacter infections caused by multidrug-resistant (MDR) isolates and not affected most of the ß-lactamases, including extended-spectrum ß-lactamases. However, their effects has been decreased gradually with the recently discovered carbapenem-hydrolysing ß-lactamase enzymes such as oxacillinases (OXA). The main reason of carbapenem resistance among Acinetobacter spp, is OXA-type beta-lactamases and OXA-51, OXA-23 and OXA-58 are frequently observed types. Especially, when OXA-type enzymes are coexistent, they reveal MDR phenotype.In this study, antimicrobial susceptibility of A. baumannii strains which had been isolated throughout over one year period and the epidemiology of carbapenem-resistant A. baumannii were evaluated; also the presence of OXA-type carbapenemases that is one of the responsible mechanisms in the carbapenem-resistance, were investigated.One hundred twenty-one A. baumannii strains isolated from miscellaneous clinical samples from hospitalized patients in Afyon Kocatepe University Hospital, between July 2008 to June 2009, were enrolled for this study. All isolates were identified by using conventional methods and advance identification done with the automatized systems. Antibiotic susceptibility tests were performed both by the Kirby-Bauer disk diffusion method and the same automatized systems.Bacterial DNA was extracted from the isolates by two different methods. At the first step, the extractes were used for optimization of blaOXA genes by in-house PCR methodology. Subsequent to this optimization process, the existance of the four groups of OXA-carbapenemase genes (blaOXA-23, blaOXA-24, blaOXA-51 and blaOXA-58) were invastigated by real time PCR.As a result of susceptibility tests, most of these isolates were found to be resistant for many antimicrobial agents, except colistin and tigecycline. The resistance against to carbapenems was observed quite high, which genarally chosen agent for the treatment of infections caused by MDR Acinetobacter species. was observed quite high. Among OXA-types enzymes responsible from carbapenem resistance; species spesific blaOXA-51 genes encoding oxacillinases showing carbapenemase activity were detected in all A. baumannii isolates, 19,0% strains with blaOXA-58 genes and 17,4 % carried blaOXA-23 genes also were detected.In conclusion, the resistance rates were observed relatively higher against antibiotics which are commonly used in clinical practices for this strains. The presence of blaOXA genes were seen the main reason of the carbapenem resistance. In this study constitutes as the first study in our hospital and also a piooner for prospective studies on carbapenem resistance and epidemiology with A. baumannii isolates.