sensitivity of levofloxacinin combination with ampicillin-sulbactam and tigecycline against multidrug-resistant acinetobacter baumannii

background and objectives: the selection of alternative treatment options with antibiotic combinations may be used for successful managing of multidrug-resistant acinetobacter baumannii . the aim of this study was to determine the synergistic effects of ampicillin-sulbactam combined with either levofloxacin or tigecycline against mdr a. baumannii. materials and methods: a total 124 of a.baumannii isolates collected from clinical samples of hospitalized patients which assessed for antibiotic susceptibility using disk diffusion method. e-test was used on 10 mdr a. baumannii isolates to determine the minimum inhibitory concentration (mic) of ampicillin-sulbactam, levofloxacin and tigecycline. any synergistic effects were evaluated at their own mic using e-test assay at 37°c for 24 hours. synergy was defined as a fractional inhibitory concentration index (fici) of ≤0.5. results: levofloxacin plus ampicillin-sulbactam combination was found to have synergistic effects (fic index: ≤0.5) in 90% of the isolates, but there was no synergistic effect for ampicillin-sulbactam/tigecycline and tigecycline/ levofloxacin combination. the antagonist effect in 50% of isolates (fic index: >2) showed in combination of levofloxacin/tigecycline. conclusion: the emergence of multidrug a. baumannii isolates requires evaluating by combination therapy. the combination of levofloxacin plus a bactericidal antibiotic such as ampicillin-sulbactam is recommended. results should be confirmed by clinical studies. keywords: acinetobacter baumannii , etest methods, microbial drug resistance, synergistic effect