In-vitro bacteriostatic and bactericidal activity of isoniazid on the Mycobacterium avium-Mycobacterium intracellulare complex.

Isoniazid inhibited the growth of Mycobacterium avium-Mycobacterium intracellulare strains at concentrations of 0.1-25 micrograms/ml and was even bactericidal for several strains. The bactericidal activity was observed in relatively susceptible strains. The susceptibility did not correlate with colonial morphology but correlated with species identification. Mycobacterium avium strains were more resistant to isoniazid than Mycobacterium intracellulare strains.