In recent years several observations have been made of the relation between colony morphology and pathogenicity of mycobacteria. Moehring and Solotorovsky [1] reported that opaque colony variants of Mycobacterium avium and other non-photochromogens were less virulent for chickens than transparent variants. Similar observations have been reported [2] on Mycobacterium intntcellulure. Schaefer, Olitzki, Davis and Cohn [3] have confirmed that the transparent variants of M. avium, sero-types I and II. caused more severe infections in chickens than the opaque variants; they also reported that in mice infected intracerebrally or by inhalation of moderate doses the opaque variants of M. avium were much less pathogenic than the transparent colony variants. In the experiments reported below more detailed observations will be presented on the pathogenicity of opaque and transparent colony variants in mice afler inoculation by the intracranial route. © 1969 S. Karger AG, Basel.
