As an alternative antimicrobial combination, danofloxacin+colistin was used for the inhibition of multidrug resistant E.coli. After evaluation of interaction between the drugs by fractional inhibitory concentration tests and time kill assays, antimicrobial activity of the combination was showed by in vitro pharmacodynamics tests (minimum bactericidal concentration and mutant prevention concentration). Post-antibiotic and post-antibiotic sub-MIC effects were also determined in this study. In synergism tests, danofloxacin+colistin was found highly synergistic (%87) against E.coli isolates from animal origin. The combination exerted bactericidal activity against all E.coli isolates and individual bactericidal activity of each compound was lower than the combination. The combination reduced mutant prevention concentration of danofloxacin and colistin up to 32 -fold. Post-antibiotic sub-MIC effects of the combination at all sub-MIC concentrations were significantly longer than the post-antibiotic effects of combination (p < 0.001), danofloxacin (p < 0.001) and colistin (p < 0.001). The results of this study showed that danofloxacin+colistin combination can be reserved as an alternative drug combination against MDR E.coli in veterinary medicine.

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