In vitroactivity of tigecycline in combination with cefoperazone–sulbactam against multidrug-resistantAcinetobacter baumannii

Over the last decade, multidrug-resistant Acinetobacter baumannii (MDRAB) has emerged as one of the most problematic nosocomial pathogens. Empirical combination therapy has become a common practice to treat patients infected with MDRAB. In vitro interactions of tigecycline with cefoperazone-sulbactam were assessed in 72 MDRAB isolates. Minimum inhibitory concentrations (MICs) were determined by broth microdilution method. Antibiotic interactions were determined by chequerboard and time-kill assays. Chequerboard analysis showed 29·2% synergy and no antagonistic interactions. Time-kill assays confirmed the synergistic interaction between two agents for three of four selected extensively drug-resistant A. baumannii (XDRAB) isolates. No antagonism was revealed by time-kill assays. Moreover, tigecycline in combination with cefoperazone-sulbactam appeared to be more effective than tigecycline in combination with sulbactam against XDRAB. In conclusion, in vitro synergistic activities of tigecycline in combination with cefoperazone-sulbactam against MDRAB were demonstrated, suggesting a superior treatment option against MDRAB.