The meaning and structure of species as applied to mycobacteria

Abstract

In an attempt to determine the nature of species amongst mycobacteria analyses at both interspecific and intraspecific levels have been performed. Over 1000 strains were examined in immunodiffusion analysis, and the majority were allotted to 20 named species on the basis of from two to eight species specific (group iv) antigens. In no case were any of these antigens shared by other species. The genus could be divided into two subgenera, one containing the slow-growing species and the other the fast-growing species, on the basis of two other groups (ii and iii) of antigens. Twenty eight strains of Mycobacterium fortuitum (ranae) were analysed by a multiplicity of methods to determine the extent of naturally occurring variation within this species. By picking off single colonies, certain variants could be selected from other variants indicating that genetically more complete strains throw off deleted mutants which may be most successful in surroundings different from those favouring the parent strain. Another mechanism of intraspecific variation, lysogeny with mycobacteriophage, was also demonstrated. The nature of species as determined by the two methods of approach are discussed, and the need for strict adherence to the rules of taxonomic nomenclature explained.