[In vitro resistance acquisition in Mycoplasma gallisepticum against ofloxacin, tylosin and spectinomycin].

To clarify a mechanism of acquired resistance of two Mycoplasma gallisepticum (MG) strains against ofloxacin (OFLX) along with tylosin (TS) and spectinomycin (SPCM) as the controls, in vitro resistance acquisition test was carried out for 10 subcultures of each strain with increasing the amount of antimicrobials, and maximum growth allowance concentrations (MAC) in 10th and primary subcultures were compared. Acquisition of resistance in the strains against OFLX was moderate and MAC of the 10th subculture increased twice for one strain and 16 times for another one as compared to that of their primary subcultures. Acquisition of resistance in the strains against TS was also moderate and MAC of the 10th subculture increased 8 times for both strains as compared to that of the primary subcultures. Acquisition of resistance against SPCM was quite different between the strains. Namely the MAC of one strain increased 512 times, while another one did not acquire any resistance.