In vitro evaluation of various antimicrobials against Mycoplasma gallisepticum and Mycoplasma synoviae by the micro-broth method, and comparison with a commercially-prepared test system

The efficacy of danofioxacin, a new quinolone antimicrobial agent, was tested in vitro by the micro-broth method with nine field strains of Mycoplasma gallisepticum (Mg) and eight of M. synoviae (Ms) and comparison was made with oxytetracycline and tylosin tartrate. The virulent S6 strain of Mg was also included for reference. All Mycoplasma strains, including a strain of Mg that was resistant to tylosin tartrate, were susceptible to danofioxacin with minimal inhibitory concentrations ranging from £ 0.008 to 0.5 μg/ml. A commercially produced test system (Sensititre®), using micro-plates whose wells were predosed with antimicrobial agents and then dried, was also investigated. Results with the same three antimicrobials were in agreement with those obtained by the micro-broth method. With the exception of the tylosin resistant strain, the Mg strains were more susceptible to erythromycin than the Ms strains. Conversely, Ms strains were susceptible to apramycin, while the Mg strains appeared to be resistant.