Various colony-formers of Mycobacterium avium-intracellulare.

Four disease-associated strains of Mycobacterium avium-intracellular isolated in our laboratory from human sputum gave rise to transparent, opaque, intermediate, and rough colony forms on cornmeal glycerol medium. Each colony-former was purified, and both the virulence to conventional ddY strain of mice and in vitro susceptibilities to various antimicrobial drugs were compared among different colony-formers. The opaque colony-formers were more susceptible to cephalothin, rifampicin, gentamicin, tobramycin, and kanamycin than the other colony-formers. Simultaneous evaluation of virulence to the mice revealed both opaque and intermediate colony-formers to be less virulent than transparent and rough colony-formers.