Comparison of in vitro activity of danofloxacin, florfenicol, oxytetracycline, spectinomycin and tilmicosin against recent field isolates of Mycoplasma bovis

The minimum inhibitory concentrations (MICs) and minimum mycoplasmacidal concentrations (MMCs) Of danofloxacin, florfenicol. oxytetracycline, spectinomycin and tilmicosin against 62 recent British field isolates of Mycoplasma bovis were determined in vitro by a broth microdilution method. The isolates were most susceptible to danofloxacin with MIC90 and MMC90 values of 0.5 mu g/ml and 1.0 mu g/ml, respectively. They were less susceptible to florfenicol with a MIC90 Of 16 mu g/ml and MMC90 Of 32 mu g/ml. Oxytetracycline and spedinomycin had only a limited effect against the majority of isolates tested with MIC(50)s of 32 mu g/ml and 4 mu g/ml, respectively and MIC(90)s of 64 mu g/ml and more than 128 mu g/ml, respectively. Nearly 20 per cent of the isolates were highly resistant to spectinomycin, and tilmicosin was ineffective, with 92 per cent of the Isolates having MIC values of 128 mu g/ml or greater. There was no evidence of resistance by M bovis to danofloxacin.