Abstract: [Objective] To improve the therapeutic efficacy of Mycoplasma bovis （M. bovis） infections in cattle. [Method] Broth micro-dilution method was used to determine the antimicrobial susceptibility of 74 strains of M. bovis isolated from Ningxia Hui Autonomous Region, China. [Result] Enrofloxacin had the narrowest MIC distribution range, with MIC₅₀ and MIC₉₀ being the smallest, followed by spectinomycin, gentamicin, and kanamycin. The resistance rate of the tested M. bovis strains to spectinomycin was the lowest （12%）, followed by enrofloxacin （22%）, while the resistance rate to gentamicin and kanamycin was the highest and identical （36%）. Isolates from cattle lungs had the highest antimicrobial resistance followed by those from joint fluids, while milk isolates had the lowest. [Conclusion] Enrofloxacin had the best antibacterial activity against the clinical isolates of M. bovis in vitro, however there was high risk in emerging of antimicrobial resistance. Dosage and duration of the antibiotics should be stressed. The strong antimicrobial resistance observed in pulmonary isolates may be related to the high probability of respiratory tract infection with M. bovis and the high frequent use of antibiotics.

Key words: Mycoplasma bovis, antimicrobial susceptibility, analysis