[Cross-resistance relationships of antituberculosis drugs in Mycobacterium avium complex]

At present, infection caused by Mycobacterium avium complex is usually treated by chemotherapy of antituberculosis drugs. However, cross-resistance relationships of antituberculosis drugs in the M. avium complex have not yet been studied. In the present study, we studied on this subject using three strains which were isolated from sputum specimens of patients who were not treated by any antituberculosis drugs: strain 13008 (serotype 20), strain 13016 (serotype 4) and strain 13034 (serotype 18). The methods used for isolating mutants resistant to rifampicin, isoniazid, ethambutol, streptomycin, kanamycin and/or enviomycin were described previously (Tsukamura, M: Kekkaku 62: 445-458, 1987). Mutants resistant to ethionamide were isolated from strains 13008 and 13016 at a rate of 10(-6) and mutants resistant to kitasamycin at a rate of 10(-5) to 10(-6) (these were not isolated from strain 13034). In contrast, mutants resistant to minocycline were isolated from strain 13034 only at a rate of 10(-4). Susceptibility testings to antituberculosis drugs were carried out as follows. Bacterial suspensions, 10 mg wet weight/ml, were prepared from ten day-old cultures of the strains growing on Ogawa egg medium slants. Each 0.02 ml-sample of the suspensions was inoculated onto Ogawa egg medium with or without a drug by a spiral loop. The media inoculated were incubated at 37 degrees C for 14 days. Minimal inhibitory concentration was determined as a concentration, on which no membraneous growth could occur. The results are shown in Tables 1 to 3. Cross-resistance relationships were observed only between ethionamide and isoniazid. Ethionamide-resistant mutant strains were resistant to isoniazid.(ABSTRACT TRUNCATED AT 250 WORDS)