Immunodiffusion analysis shows that Mycobacterium paratuberculosis and other mycobactin-dependent mycobacteria are variants of Mycobacterium avium.

Antigenic analysis by immunodiffusion has been applied to 74 strains of mycobactin-dependent mycobacteria. Thirty-eight strains were of Mycobacterium paratuberculosis from cases of Johne's disease of cattle or goats. The remaining cultures were obtained from a variety of animals and included the wood pigeon bacillus. Rabbit antisera were raised to some of the strains and these, together with antisera to M. avium and M. intracellulare, were used to examine sonicate preparations of all the cultures. All were found to be antigenically identical with M. avium and none were found to belong to M. intracellulare. A predominance of the cultures from Johne's disease belonged to the potential brunense subspecies of M. avium, and the remainder together with the majority of the other mycobactin-dependent strains belonged to the type subspecies. In view of these findings the separate species status of M. paratuberculosis is refuted and some difficulty remains in the nomenclature of strains giving rise to Johne's disease.