PAPERS & ARTICLES Antibiotic susceptibilities of recent isolates of Mycopasma bovis in Belgium

The susceptibilities of 40 recent Belgian field isolates of Mycoplasma bovis to 10 antimicrobial agents were assessed. Tiamulin was the most active antimicrobial agent againstM bovis, with an initial inhibitory concentration (IIcso) of 0-06 pig/ml, but it is not licensed for the treatment of cattle. All three fluoroquinolones tested (danofloxacin, enrofloxacin and marbofloxacin) were effective against strains ofM bovis, and had a minimum mycoplasmacidal concentration (MMcso) less than or equal to 1 pg/mI. Gentamicin was poorly effective, having an IIC50 of 8 pg/mI. Many strains ofM bovis were resistant to tylosin, spectinomycin, lincomycin, tetracycline and oxytetracycline. DESPITE antibiotic therapy, bovine respiratory infections continue to be among the most costly diseases on farms (Miskimins and others 1995). Factors such as transport, high stocking rates and poor ventilation can predispose calves to respiratory infections (Martin 1983). Several agents have been implicated as primary causes of calfpneumonia, but the syn-drome is commonly multifactorial; viruses and bacteria can interact to induce fatal diseases (Gourlay and Houghton 1985, Virtala and others 1996, Alkan and others 2000, Fulton and others 2000). Among the respiratory mycoplasmas, Mycoplasma bovis has been found to be the species most com-monly associated with calf pneumonia in Europe and Nort