Acinetobacter baumannii is one of the major opportunistic pathogens with increasing clinical significance, particularly in the Hospital setting. Objectives: The study aimed to analyze the antibiotic resistance determinants in multidrug-resistant A. baumannii (MDRAB) isolates collected after an outbreak, with regard to the infection prevention control (IPC) interventions to eradicate the outbreak. Methods: Thirty nine isolates of MDRAB were collected during six months of the study after the

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... eak. Infection prevention control was successful only for the first three months after the intervention. Antimicrobial susceptibility testing and minimum inhibitory concentrations (MICs) were determined by E-test. In addition, various resistance genes and the clonal relatedness of the isolates were performed by PCR and REP-PCR. Results: All isolates were MDRAB while being susceptible to colistin. The prevalence of blaADC, blaTEM, blaOXA24, blaVIM, and blaIMP was 82%, 100%, 70%, 61%, and 5%, respectively. blaOXA51, blaOXA23, and ISAba1 were detected in all isolates, but blaOXA58 was not. Moreover, ISAba1 was located upstream to blaOXA23 and blaADC in 100% and 38.4% of the isolates, respectively. The most prevalent AME was aadB (100%). Even though adeB and tetB efflux pumps were found in 100% and 95% of the isolates, respectively, tetA was not characterized. REP-PCR revealed five clusters of which, approximately 51% of the strains belonged to cluster C. Conclusions: Regarding the molecular approach, the effectiveness of IPC and epidemiological context has been identified. Stringent infection-control measures are urgent to restrict the outbreak.