Catalase-peroxidase -resistance to isoniazid:mediated primarily by mutations of the katg gene, resulting in the loss of the catalase-peroxidase enzyme that is required for the activation of isoniazid-overexpression of inhaisoniazid=isonicotinic acid hydrazide (inh)bactericidalnarrow-spectrummechanism of action:katg gene in mycobacteria encodes catalase-peroxidase in mycobacteria. catalase-peroxidase converts inh to active form.activated form of inh inactivates the enzymes involved in mycolic acid synthesis enoyl-acyl carrrier protein(acp) reductase (encoded by inha) and beta-ketoacyl-acp synthase (encoded by kasa), resulting in the inhibition of mycolic acid sysnthesis, and subsequently, inhibition of call wall synthesis.