Susceptibilities of Mycoplasma hominis, M. pneumoniae, and Ureaplasma urealyticum to GAR-936, Dalfopristin, Dirithromycin, Evernimicin, Gatifloxacin, Linezolid, Moxifloxacin, Quinupristin-Dalfopristin, and Telithromycin Compared to Their Susceptibilities to Reference Macrolides, Tetracyclines, and Quinolones

The susceptibilities of Mycoplasma hominis, Mycoplasma pneumoniae, and Ureaplasma urealyticum to eight new antimicrobial agents were determined by agar dilution. M. pneumoniae was susceptible to the new glycylcycline GAR-936 at 0.12 μg/ml and evernimicin at 4 μg/ml, but it was resistant to linezolid. It was most susceptible to dirithromycin, quinupristin-dalfopristin, telithromycin, reference macrolides, and josamycin. M. hominis was susceptible to linezolid, evernimicin, and GAR-936. It was resistant to macrolides and the ketolide telithromycin but susceptible to quinupristin-dalfopristin and josamycin. U. urealyticum was susceptible to evernimicin (8 to 16 μg/ml) and resistant to linezolid. It was less susceptible to GAR-936 (4.0 μg/ml) than to tetracycline (0.5 μg/ml). Telithromycin and quinupristin-dalfopristin were the most active agents against ureaplasmas (0.06 μg/ml). The new quinolone gatifloxacin was active against M. pneumoniae and M. hominis at 0.12 to 0.25 μg/ml and active against ureaplasmas at 1.0 μg/ml. The MICs of macrolides were markedly affected by pH, with an 8- to 32-fold increase in the susceptibility of M. pneumoniae as the pH increased from 6.9 to 7.8. A similar increase in susceptibility with increasing pH was also observed with ureaplasmas. Tetracyclines showed a fourfold increase of activity as the pH decreased 1 U, whereas GAR-936 showed a fourfold decrease in activity with a decrease in pH.