In vitro susceptibilities of Mycobacterium tuberculosis to 10 antimicrobial agents

After preliminary in vitro screening of 10 antimicrobial agents against Mycobacterium tuberculosis, the MICs of the 6 most promising agents against 27 clinical isolates were determined by agar dilution. The two quinolone compounds tested (difloxacin and A-56620) were the most active, each inhibiting 50% of the strains at concentrations of 4 micrograms/ml. M. tuberculosis strains previously shown to be resistant to isoniazid, streptomycin, rifampin, or ethambutol were as susceptible to these quinolone compounds as susceptible strains.