Abstract: Objective To explore the induction of L-forms of Mycobacterium abscessi using isoniazid. Methods Mycobacterium
abscessi 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. Results 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. Conclusion Isoniazid can induce the L-forms of mycobacterium abscessi for use in studies of multidrug
resistance and treatment of the bacteria.