ABSTRACT
Objective: Acinetobacter baumannii species cause nosocomial infections and can subsequently develop multidrug resistance [MDR]. The objective of this study was to evaluate the susceptibility of A. baumannii to a novel combination of colistin and tigecycline, which may provide a faster and more efficacious treatment via a synergistic effect
Methods: We included 50 MDR A. baumannii samples that were isolated in our clinics between 2009 and 2014. We used broth microdilution [BMD] and the E-test to evaluate the effects of colistin and tigecycline, and the E-test to assess the interaction of the colistin-tigecycline combination. The interaction between the two antibiotics was evaluated using the fractional inhibition concentration [FIC] index and was classified as follows: FIC/=4, antagonistic
Results: No tigecycline and colistin resistance was determined by BMD or E-test. The interaction between colistin and tigecycline, when used in combination, was 2% synergistic, 6% additive, 88% indifferent, and 4% antagonistic
Conclusion: Although combination therapy is suggested for MDR A. baumannii infections, our results suggest that the synergistic effect of the colistin-tigecycline combination is insufficient to make it an optimal treatment choice