Taxonomic characteristics of so-called 'form 2 mycobacteria'.

SUMMARY: Two strains of rapidly growing spore-forming bacteria were obtained from cultures of Mycobacterium tuberculosis and identified as so-called ‘form 2 mycobacteria’ (Csillag, 1961). The properties of these and of two similar strains received from Dr A. Csillag were investigated, and compared with those of NCTC strains of the genus Bacillus. All four ‘form 2’ strains were almost identical in character, and differed from M. tuberculosis in many respects, rendering it highly unlikely that they were genetically derived from the mycobacterial cultures in which they were found. They were identified as strains of Bacillus licheniformis. It is considered that ‘form 2’ organisms are not part of a complex mycobacterial life-cycle, as has been suggested, but are contaminants.