We investigated the in-vitro and in-vivo activity of a new quinolone AM-1155 against Mycoplasma pneumoniae, and compared it with ofloxacin, ciprofloxacin, lomefloxacin, tosufloxacin, erythromycin and minocycline. AM-1155 was the most potent agent in vitro of the quinolones tested. Its pre-treatment minimal inhibitory concentrations for 90% of the 41 strains (MIC90) was 0.06 mg/L.In contrast, pre-treatment MIC90 values for ofloxacin, ciprofloxacin, lomefloxacin, tosufloxacin, erythromycin, and minocycline were 1, 1, 2, 0.5, 0.0156, and 0.5 mg/L, respectively. Post-treatments MIC90s, which may reflect mycoplasmacidal potency, of AM-1155, ofloxacin, ciprofloxacin, lomefloxacin, tosufloxacin, erythromycin and minocycline were 0.125, 1, 2, 4, 0.5, 0.125 and 4 mg/L, respectively.In-vitro activities of antimicrobial agents were assessed in an experimental pulmonary infection model in Syrian golden hamsters. AM-1155 was the most effective agent among five antimicrobial agents (AM-1155, ofloxacin, tosufloxacin, erythromycin, minocycline) tested in terms of reduction in viable M. pneumoniae cells and in reducing macroscopic lung lesions. These results suggest that AM-1155 will be a useful antimicrobial agent for the treatment of M. pneumoniae infections.
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