[In vitro susceptibilities of Mycobacterium avium and Mycobacterium intracellulare to various drugs].

Mycobacterium avium and M. intracellulare isolated from patients infected with M. avium complex (MAC), which were identified by Gen-Probe Rapid Diagnostic System for the MAC, were studied for susceptibility to various antimicrobial agents, including rifampicin, rifabutin, kanamycin, streptomycin, amikacin, ethambutol, clofazimine, isoniazid, ofloxacin, ciprofloxacin and cycloserine. Ratio of resistant strains to test strains to a given agent at prescribed concentration in cases of M. avium and M. intracellulare was compared with each other. Test strains of M. avium were more resistant to rifampicin, rifabutin, kanamycin, streptomycin, amikacin, ethambutol and clofazimine than test strains of M. intracellulare. Conversely, the M. avium strains were more susceptible to ofloxacin, ciprofloxacin and cycloserine than M. intracellulare strains. The difference in the drug susceptibility between M. avium and M. intracellulare was statistically significant by chi 2-test (P less than 0.005-0.05). There was no statistically significant difference between the two MAC species with respect to the susceptibility to isoniazid.