Antimicrobial Susceptibility of Caprine and Ovine Mycoplasma ovipneumoniae Isolates

The objective of this study was to determine the minimum inhibitory concentrations (MICs) of nine antimicrobials (enrofloxacin, ciprofloxacin, norfloxacin, gentamicin, spectinomycin, oxytetracycline, tylosin, florfenicol, and tiamulin) against 24 Mycoplasma ovipneumoniae isolates obtained from sheep and goats and to compare the resulting antimicrobial profiles. Enrofloxacin and ciprofloxacin had the lowest MIC₅₀ values (<0.03 μg/mL) and MIC₉₀ values (0.25 μg/mL) for all tested isolates. The highest MIC₅₀ value (2 μg/mL) was obtained for florfenicol, while oxytetracycline and tylosin exhibited the highest MIC₉₀ values (16 μg/mL). The MIC values for all fluoroquinolones and oxytetracycline were significantly lower for sheep isolates. Sheep isolates were considerably more susceptible to norfloxacin and tylosin than were goat isolates. This study demonstrated differences in antimicrobial susceptibilities between sheep and goat isolates, revealing M. ovipneumoniae in goat isolates to be less susceptible. The results suggest a possible link between antimicrobial profiles of M. ovipneumoniae isolates and their host ruminant species.