In Vitro Activities Of Cefoperazone-sulbactam, Sitafloxacin,and Polymyxin E In Combination Against Extensively Drug-resistant Acinetobacter Baumannii

Abjective:The aim of this study was to evaluate the in vitro activities of combinations of sitafloxacin, cefoperazone-sulbactaml:land polymyxin E against extensively drug-resistant Acinetobacter baumannii (XDR-A. baumannii).Methods:Twenty-two strains of XDR-^4. baumannii were isolated from clinical patients. All the XDR strains were identified and selected by VITEK 2 compact analyzer and Kirby-Bauer (K-B) method according to the guidelines of the CLSI.The minimum inhibitory concentration (MIC)s of Sitafloxacin, cefoperazone-sulbactaml:1, polymyxin E in single-use against XDR-A. baumannii were determined by the broth microdilution method, and the MICs in combination were determined by the checkerboard method. According to the MIC results, the values of fractional inhibitory concentration (FIC) and FIC index (FICI) were calculated. The values of FICI were interpreted as follows:<0.5, synergy;>0.5 to<1, partial synergy; 1, addition;>1 to<4, indifference; and≥4, antagonism.Results:In our study, the MIC of Sitafloxacin was0.25-16μg/ml,the MIC of cefoperazone-sulbactam (1:1) was 4.0/4.0-128/128μg/ml, the MIC of polymyxin E was 0.5-8.0μg/ml. most combinations of the three drugs were synergy, partial synergy or addition effects when compared to the drugs used alone.Conclusion:The present study showed that sitafloxacin and polymyxin E, especially sitafloxacin, had good activity against XDR-A. Baumannii in vitro when drug used alone. Cefoperazone-sulbactam alone against these strains showed less efficacious. Combinations of polymyxin E with either sitafloxacin or cefoperazone-sulbactam showed better activity against XDR isolates in vitro than single drug and the MIC values reduced significantly. It was similar to the other two drugs. The FICI values showed that most combinations of the three antimicrobial agents were synergy, Partial synergy or addition effects against these XDR isolates when compared to the monotherapy. No strains in antagonism were found.The combinations may be alternative options for treating infections of XDR-A baumannii.