Effects of isoniazid on viability, cell morphologies and acid fastness properties of Mycobacterium avium NCTC 8559 during the growth cycle

Our previous study demonstrated that the effects of isoniazid (INH) on Mycobacterium tuberculosis at the cellular level varied according to the growth phases. In this study, the variations in the INH action on M. avium strain NCTC 8559 are reported. M. avium cells grown on Middlebrook 7H10 agar were harvested at different stages of their growth cycle, exposed to the minimum inhibitory concentration of INH, stained with acid-fast staining for morphological changes and acid fastness properties, and the number of colonies were evaluated for viability studies. The study demonstrated that M. avium NCTC 8559 cells at the initial and fragmentation stages of the growth cycle were most susceptible to INH.