In vitro susceptibilities of rapidly growing mycobacteria to newer antimicrobial agents

The in vitro antimicrobial susceptibilities of 42 isolates of rapidly growing mycobacteria (Mycobacterium fortuitum, M. chelonae, and Mycobacterium species [other than M. fortuitum and M. chelonae]) to nine quinolones, including newer agents, two new aminoglycosides, and an aminocyclitol (trospectomycin) were determined by a broth microdilution method. The new quinolones, PD 117596, PD 127391, and PD 117558, showed excellent in vitro activities against M. fortuitum (MICs for 90% of isolates [MIC₉₀s], 0.06, 0.06, and 0.12 μg/ml, respectively). The MIC₉₀ of ciprofloxacin for M. fortuitum was 0.5 μg/ml. Only 14 to 28% of isolates of M. chelonae were susceptible to various quinolones. Most isolates of all three species were susceptible to the new aminoglycosides SCH 21420 and SCH 22591. The MIC₉₀s of trospectomycin were 8 μg/ml for M. chelonae, 32 μg/ml for Mycobacterium species, and >64 μg/ml for M. fortuitum.