Sensitivity of Certain Porcine and Bovine Mycoplasmas to Antimicrobial Agents in a Liquid Medium Test Compared to a Disc Assay

The sensitivity of some porcine and bovine mycoplasmas to potent antimicrobial agents was examined. Minimal inhibitory concentration (MIC) values were estimated for M. hyosynoviae, M. hyopneumoniae, M. dispar and M. bovis against enrofloxacin, lincomycin, tetracycline, tiamulin and tylosin, in a liquid medium test and in a disc assay. All 6 examined strains of each species and the respective type strains were significantly inhibited. The greatest sensitivity was noted for tiamulin against strains of M. hyosynoviae with a final MIC50 broth value of 0.025 µg ml−1 and disc value of 0.03 µg per disc. Enrofloxacin was found very potent against M. hyopneumoniae with a final MIC50 of 0.025 µg ml−1 and 0.1 µg per disc, and for M. dispar with 0.05 µg ml−1 and 0.03 µg per disc. Most disc assay estimates in ug per disc were similar to or moderately greater than corresponding final broth figures in µg ml−1. It may be possible to convert observed disc assay values into representative final broth MIC values for use in the clinic.