Pathogenicity of transparent, opaque, and rough variants of Mycobacterium avium in chickens and mice.

The pathogenicity of transparent, opaque, and rough variants of different strains of Mycobacterium avium was determined in chickens by intravenous inoculation of more than 100 million bacterial viable units and in mice by airborne infection with more than 10 thousand viable units. The seven transparent variants were pathogenic in both chickens and mice. Only two of five opaque variants were pathogenic for chickens, and only two of seven opaque variants were pathogenic for mice. The two pathogenic opaque variants differed from the other opaque variants by having dysgonic growth. Two rough variants were pathogenic for chickens, and four rough variants were pathogenic for mice, causing a more severe infection than the transparent variants. These observations have led to a hypothesis regarding the mechanism of pathogenicity of M. avium.