Copyright q 1995, American Society for Microbiology In Vitro Antibacterial Activity of DU-6859a, a New Fluoroquinolone

The in vitro antibacterial activity of DU-6859a, a new fluoroquinolone, against a wide variety of clinical isolates was evaluated and compared with those of tosufloxacin, ofloxacin, ciprofloxacin, and sparfloxacin. DU-6859a showed potent broad-spectrum activity against gram-positive, gram-negative, and anaerobic bacte-ria, and its activity was greater than those of the control quinolones. By comparison of MICs at which 90 % of strains are inhibited, DU-6859a had potent activity against bacteria resistant to the control quinolones. The time-killing curves of quinolones showed that the number of viable cells decreased rapidly during 2 to 4 h of incubation, and regrowth was not seen even after 8 h of incubation. At a concentration of four times the MIC, the frequencies of appearance of spontaneous mutants of Staphylococcus aureus, Escherichia coli, and Pseudo-monas aeruginosa resistant to DU-6859a were %4.0 3 1029 to 1.9 3 1028. The 50 % inhibitory concentrations of DU-6859a were 0.86 and 1.05 mg/ml for the supercoiling activities of DNA gyrases isolated from E. coli and P. aeruginosa, respectively. The rank order of the 50 % inhibitory concentrations observed for both DNA gyrases roughly paralleled the MICs. A number of new quinolone antibacterial agents such as tosufloxacin (1), ofloxacin (8), ciprofloxacin (9), and sparfloxa-cin (5) have been developed and introduced into the market