Plasmid deoxyribonucleic acid and translucent-to-opaque variation in Mycobacterium intracellulare 103

After treatment with mitomycin C and other antibacterial agents, a translucent, smooth-colony-forming mycobacterium, isolated from sputum and designated as M. intracellulare strain 103, gave rise to variants forming opaque colonies. These opaque variants were more sensitive streptomycin, kanamycin, viomycin, and rifampin than were the wild-type translucent variants. Plasmid deoxyribonucleic acids taken from translucent strain cells and from cells of certain opaque variants were analyzed by agarose gel electrophoresis. Two plasmids of molecular weights of approximately 2 X 10⁶ and 50 X 10⁶, respectively, were found in the wild-type translucent cells; one of them, the 2 X 10⁶-molecular-weight plasmid, was always missing from deoxyribonucleic acids of the opaque variant cells. The results suggested that translucent colonial appearance and antibiotic resistance of the strain are plasmid-determined functions.