Sensitivity of levofloxacin in 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.