[Antimycobacterial susceptibility against nontuberculous mycobacteria using brothmic NTM]

Recently the incidence of pulmonary nontuberculous mycobacteria infection has increased among patients not only implicated with AIDS, but also without predisposing conditions. However, an effective antimicrobial therapy for the disease has not been established yet, because of the absence of highly active therapeutic drugs. We compared the in vitro antimicrobial activities of five antituberculous drugs, clarithromycin and fluoroquinolones against 92 clinical isolates belonging to three species of slowly growing nontuberculous mycobacteria.

M. avium (31 strains), M. intracellulare (44 strains), and M. kansasii (17 strains), all of which were isolated from sputum specimens of previously untreated patients with pulmonary nontuberculous mycobacteria infection, were used. The eight agents tested were streptomycin, ethambutol, kanamycin, isoniazid, rifampicin, clarithromycin, levofloxacin and gatifloxacin. The drug susceptibility of these strains in terms of MIC (minimum inhibitory concentration) was determined by BrothMIC NTM.

The MICs of rifampicin, clarithromycin, levofloxacin and gatifloxacin for all three species were low and gatifloxacin was more active than levofloxacin between two fluoroquinolones. Regarding clarithromycin, 100% of the strains were susceptible to 2 micrograms/ml or less and none of the strains were resistant on this level. In contrast, the MICs of ethambutol and isoniazid for M. avium and M. intracellulare were high and less active in vitro than the other antimicrobial agents.

These MIC studies suggest that rifampicin, clarithromycin, levofloxacin, and gatifloxacin have excellent in vitro antimicrobial activities against M. avium, M. intracellulare and M. kansasii and especially clarithromycin may be very useful as a drug therapy for previously untreated patients. In the treatment of pulmonary nontuberculous mycobacterium infection, further studies are needed to evaluate the clinical effects of these drugs and to observe the drug resistance, on the basis of the results of the drug susceptibility test by BrothMIC NTM.