OXA-type Carbapenemases and Susceptibility of Colistin and Tigecycline Among Carbapenem-Resistant Acinetobacter Baumannii Isolates from Patients with Bacteremia in Turkey

Background: Carbapenem-resistant Acinetobacter baumannii (CRAB) has emerged as one of the most troublesome pathogens in healthcare settings worldwide. The present study was conducted to analyze the genes encoding resistance to carbapenems and to determine in vitro activity of colistin and tigecycline against CRAB isolates from blood culture of hospitalized patients at Istanbul University Cerrahpasa Medical School hospital. Methods: Between January 2012 and June 2014, a total of 72 CRAB isolates were isolated by conventional methods from blood cultures of patients with bacteremia who were hospitalized in intensive care units and in various departments of the hospital. The isolates were confirmed using a Phoenix automated system. Antibiotic susceptibilities were determined by disk diffusion method and Etest. Molecular detection of resistance genes were screened by multiplex real time polymerase chain reaction (qPCR) and PCR parameters. Results: CRAB isolates were highly resistant to tetracycline (86.1%), trimethoprim/sulfamethoxazole (84.7%), ceftazidime (83.3%), cefepime (81.9%), ciprofloxacin (81.9%), amikacin (75.0%), piperacillin/tazobactam (75.0%), cefotaxime (72.2%), and gentamicin (69.4%). Tigecycline and colistin resistance were not detected. MIC50 and MIC90 of tigecycline (MIC ranges 0.016 - 1 mu g/mL) and colistin (MIC ranges 0.125 - 1.5 mu g/mL) were found to be 0.5 mu g/mL and 1 mu g/mL, respectively. All isolates were positive for OXA-51 that shows molecular identification of A. baumannii. Fifty-one (70.8%) and 2 (2.8%) of these isolates were positive for OXA-23 and OXA-58 genes, respectively. Conclusions: This study indicated the most of the CRAB isolates in our hospital carry the OXA-23 gene. Colistin and tigecycline resistance were not detected. However, significant effort must be done to prevent the spread of OXA-23-producing CRAB-isolates and continuous monitoring of drug resistance is necessary in clinical settings.