DS-8587 is a DNA topoisomerase inhibitor. DS-8587 exhibits potent antibacterial activity against quinolone-resistant A. baumannii isolates that harbor mutations in quinolone resistance-determining regions. DS-8587 significantly reduces the number of viable bacteria in a murine model of F. necrophorum-induced liver abscess. In the presence of the efflux pump inhibitor 1-(1-napthylmethyl)-piperazine, no significant changes were observed in the MIC for DS-8587.