Bachground: Acinetobacter baumannii as an opportunistic gram-negative bacterium is the leading cause of nosocomial infections, especially in patients admitted to intensive care units. Given the increment of resistance to multidrug-resistant A. baumannii isolates  and the lack of suitable treatment options, the needs for investigating new drugs or combinations of drugs are felt. The aim of this study was to determine the synergistic effects of Vancomycin in combination with Tigecycline, Levofloxacine, Gentamycin, Colistin and Meropenem and the combination of Colistin with Meropenem and Rifampin against the infections caused by multidrug-resistance A. baumanni isolates.

Material and Methods: This experimental study was done on  multi-drug A. baumannii isolates (n=10) from blood cultures, tracheal tube samples, sputum and the urine of patients hospitalized in the Beheshti Hospital between June 2014 and June 2015. Antibiotic susceptibility testing was performed by disk diffusion method according to CLSI standards. synergy testing was done by disk diffusion method.

Results: On combining the Vancomycin with Tigecycline Levofloxacine, Gentamycin, Colistin and Meropenem, no synergy was detected. The combination of Colistin/Meropenem and Colistin/Rifampin were indifferent with no synergistic effect.

Conclusion: The combination of other antibiotics could be considered as an alternative antibiotic treatment for multi-drug A. baumannii isolates. Due to the smaller sample size in our study, for taking better results the future studies should focus on well-designed in vitro models on a large scale.