Antimicrobial susceptibility of pathogenic mycoplasmas in chickens in Asia

Mycoplasma synoviae (n = 26) and M. gallisepticum (n = 11) isolates were gained from 164 clinical samples collected from China, India, Indonesia, Malaysia, Philippines, Republic of Korea and Thailand. Most isolates were from commercial chicken production systems. A method of filtering (0.45 μm) samples immediately after collection was convenient allowing over a week for transit to the laboratory. Minimum inhibitory concentrations (MICs) were characterized by a broth microdilution method to enrofloxacin, difloxacin, oxytetracycline, chlortetracycline, doxycycline, tylosin, tilmicosin, tylvalosin, tiamulin, florfenicol, lincomycin, spectinomycin and lincomycin and spectinomycin combination (1:2). Increased MICs to various antimicrobials were seen in different isolates but appeared largely unrelated to the antimicrobial treatment histories. Overall, the results were similar to other MIC surveys around the world. Generally, low MICs to tetracyclines, tiamulin and tylvalosin were observed. Increased tilmicosin MICs were observed in both M. synoviae and M. gallisepticum isolates (≥64 μg/ml MIC₉₀ values) and this was seen in all isolates with high tylosin MICs. Increases in lincomycin MICs were mostly associated with increases in tilmicosin MICs. The results also suggested that antimicrobial use after mycoplasma vaccination may interfere with vaccine strain persistence and efficacy (field strains were more commonly observed in flocks that had treatments after vaccination) and this area warrants more investigation. The study shows that isolation and MIC determination can be done from remote locations and suggests that this may provide information that will allow more effective use of antimicrobials or other methods of control of avian mycoplasma in chickens (e.g. live vaccines) and therefore more responsible use of antimicrobials from a one health perspective.