RESUMO
<p><b>OBJECTIVE</b>To explore the induction of L-forms of Mycobacterium abscess using isoniazid.</p><p><b>METHODS</b>Mycobacterium abscess were cultured in aqueous culture media in the presence or absence of 128 µg/ml isoniazid. The culture media containing isoniazid were filtered with 0.45 µm membrane, and the filtrate was subcultured in nutrient agar media for reversion. The isoniazid-free and isoniazid-containing media and the reversion bacteria were observed for cell wall integrity by cell wall staining and transmission electron microscopy, and the microstructures of the cell surfaces were observed by scanning electron microscopy. The isoniazid-containing culture was subcultured in L-form agar media, and the isoniazid-free culture and the reversed bacteria in nutrient agar media to observe the colony morphology. The reversed and non-induced bacteria were identified for 16S rDNA.</p><p><b>RESULTS</b>The bacteria induced with 128 µg/ml isoniazid showed cell wall defect, presenting with a spherical cell morphology and typical fried egg-like colonies in L-form agar media, while in isoniazid-free cultures, the cells showed intact cell walls with rod-like shapes and round colony morphologies on nutrient agar. The reversed bacteria, showing also intact cell walls with rod-like shapes and round colonies on nutrient agar, had identical 16S rDNA with the non-induced bacteria.</p><p><b>CONCLUSION</b>Isoniazid can induce the L-forms of mycobacterium abscess for use in studies of multidrug resistance and treatment of the bacteria.</p>