The in vitro activity of dual-acting antibacterial Ro 23-9424 was determined by the agar dilution method against 126 clinical isolates of Brucella melitensis. It was compared with fleroxacin, ciprofloxacin and five conventional drugs. MIC50 and MIC90 for Ro 23-9424 were 1.0 and 4.0 mg/l, respectively, as compared with 0.25 and 0.5 mg/l for fleroxacin and ciprofloxacin. One strain which was resistant to other fluoroquinolones, with an MIC of > 8.0 mg/l, did not show cross-resistance to Ro 23-9424 and had an MIC of 4.0 mg/l. All the strains were susceptible to conventional drugs like gentamicin, streptomycin rifampicin, tetracycline and trimethoprim-sulfamethoxazole, with MICs ranging between 0.12 and 2.0 mg/l. Ro 23-9424 did not exhibit in vitro synergy with any of the conventional drugs.
The antimicrobial activity of the new fluoroquinolone rufloxacin (MF 934) was evaluated by a standardized agar dilution method against recent clinical isolates of Salmonella typhi (67 strains) and Brucella melitensis (108 isolates). The results were compared with 5 other commercially available or investigational fluoroquinolones. All the isolates of S. typhi were inhibited by 1.0 mg/l of rufloxacin as compared to 4-8 mg/l for B. melitensis. Minimum inhibitory concentrations of rufloxacin against both S. typhi and B. melitensis were 4-16 times higher than those of other fluoroquinolones.
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