Relationship between <i>Mycobacterium</i> and <i>Nocardia</i>

ABSTRACTNumerical classification was carried out using a “hypothetical mean organism” and 11 species of the genus Mycobacterium and 6 species of the genus Nocardia. Statistical survey of the results indicated the presence of three taxonomic groups, the slowly growing mycobacteria, the rapidly growing mycobacteria and nocardiae. The present author had previously divided the genus Mycobacterium into two subgenera, Mycobacterium and Mycomycobacterium, which corresponded approximately to slowly growing mycobacteria and rapidly growing mycobacteria, respectively. In the numerical classification, these two subgenera behaved as if they were two genera. It was suggested thus that these two subgenera of genus Mycobacterium should be transferred to two genera. Beside morphological characters, three biochemical characters were shown to be useful for differentiating between rapidly growing mycobacteria and nocardiae: (1) A two‐week arylsulfatase activity; (2) Acid formation from mannose; (3) Utilization for growth of trimethylene diamine as a simultaneous nitrogen and carbon source.