The Mycococcus Form of Mycobacteria

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Abstract
Cultures of form 2 mycobacteria, which had been recently isolated from form 1 of strains of Mycobacterium tuberculosis and atypical mycobacteria, were cultivated on nutrient agar in screw-capped bottles and kept unopened for 6 weeks at room temperature. Gram-positive granules developed in organisms which had penetrated into the medium. When these organisms were incubated in digest broth at 37[degree] with intermittent aeration, the granules were liberated into the medium and gradually increased in size to that of a small coccus. After a resting period of about 2 weeks, the "cocci" started to multiply independently, forming diplococci and tetrads. At this stage the cocci yielded colonies on subculture on nutrient agar. The cocci were identified as members of the genus Mycococcus, family Myco-bacteriaceae, order Mycobacteriales (Krassilnikov, 1959). Mycococci were not obtained in broth cultures which were either not aerated or were aerated frequently or continuously. Prolonged subcultivation of the parent form 2 strains on nutrient agar prevented the development of mycococci in broth. Evidence, such as the failure to isolate mycococci from uninoculated but aerated media, is submitted that the mycococci were not contaminants. Previous work on isolation of similar cocci from different members of the order Actinomycetales, including human and bovine strains of Mycobacterium tuberculosis is reviewed.