Abstract
Ten of 28 strain of Mycobacterium fortuitum (ranae) were found to be associated with bacteriophage; three were pseudolysogenic, one liberated a phage that lysed a sensitive indicator strain, two liberated morphologically complete phages that did not lyse any of the strains used in this study and four liberated morphologically defective phages. The lysogenic and defectively lysogenic strains showed anomalies in cultural, biochemical and antigenic properties and in susceptibility to superinfecting phages. In view of the high frequency of lysogeny found in M. fortuitum, the role of bacteriophage in the variation of properties, including pathogenicity, of mycobacteria of greater clinical importance merits further consideration.