Numerical taxonomy and cooperative studies: roles and limits.

Because of the wide array of specialized tests needed for classification of mycobacteria and the complexity of some of these tests, the International Working Group on Mycobacterial Taxonomy was organized in 1967 to conduct cooperative studies and provide a broad data base for numerical taxonomic analysis of the genus. Certain parameters, such as immunologic properties and lipid composition, were withheld from the numerical analyses to provide independent corroboration of the observed clustering. Overall, these studies have yielded confirmation of the validity of many species, as well as detailed description of these species. The numerical analyses do not resolve all taxonomic questions in the genus Mycobacterium, but they do provide phylogenetic hypotheses based on phenetic clustering. These hypotheses presently are being tested by techniques for measuring DNA relatedness and protein sequence conservation. Concurrently, cooperative studies are continuing in order to provide adequate description of some of the more obscure mycobacterial species.