Anti-Brucella activity of Ro 23-9424, a dual-action antibacterial

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.