[Relative relatedness of 11 mycobacteria species by microplate hybridization methods considering delta Tm].

Intra-species variance within Mycobacterium xenopi, Mycobacterium gordonae or Mycobacterium szulgai has been reported in identification employing chemotaxonomic characteristics, 16 S rRNA gene sequences or relative relatedness (relative color index) of genomic DNA-DNA Hybridization. Genomic DNA-DNA reassociation at the constant temperature was found to be unreliable for classification of mycobacterial species. However, nonspecific DNA reassociation could be avoided by hybridization at 56 degrees C after 45 degrees C overnight, and this technique was named delta DDH method in the preceding paper. The present report shows relative relatedness (relative color index) of genomic DNA in delta DDH method among mycobacterial species. Relative relatedness was below 70% among BCG, M. kansasii, M. simiae, M. asiaticum, M. szulgai, M. gordonae, M. xenopi and M. nonchromogenicum. The results satisfied the criteria for bacterial classification, which was proposed by the International Committee for Systematic Bacteriology in 1987. In regard to Mycobacterium avium complex, relative relatedness between M. avium and M. intracellulare were approximately 75%. It appeared that M. avium and M. intracellulare could be classified into one species. It has been recognized, moreover, that there are intermediate strains between M. avium and M. intracellulare. Previously, numerical classification raised a concept of Mycobacterium avium-intracellulare-scrofulaceum complex. The present study revealed that relative relatedness of M. avium and of M. intracellulare to M. scrofulaceum were around 75%, while the percentiles of M. scrofulaceum relative to M. avium and that to M. intracellulare were both less than 50%. The relative relatedness of M. ulcerans against M. marinum was nearly 65%, whereas the relative relatedness of M. marinum against M. ulcerans was approximately 90%. The data may be partly explained by the horizontal gene transfer mechanism.