SEMANTIDE-BASED AND CHEMOTAXONOMY-BASED ANALYSES OF SOME PROBLEMATIC PHENOTYPIC CLUSTERS OF SLOWLY GROWING MYCOBACTERIA, A COOPERATIVE STUDY OF THE INTERNATIONAL WORKING GROUP ON MYCOBACTERIAL TAXONOMY

During previous cooperative numerical taxonomic studies of slowly grow ing mycobacteria, the International Working Group on Mycobacterial Tax onomy described a number of strains whose taxonomic status was ambiguo us. A new study of DNA, RNA, and proteins from 66 of these organisms w as performed to correlate their properties with phenotypic clustering behavior; the results of this study permitted 51 of the strains studie d to be assigned to known species. The methods used to characterize th e semantides included nucleotide sequencing and assessment of levels o f semantide relatedness by affinity binding techniques, including whol e DNA-DNA hybridization, probe hybridization, and antibody binding. Th ere was good overall agreement between the phenotypic and chemotaxonom ic clusters and the groups of organisms identified by semantide analys es. Our results supported the conclusion that we should continue to re ly on polyphasic taxonomy to provide satisfactory systematic resolutio n of members of the genus Mycobacterium. We identified no single 16S r RNA interstrain nucleotide sequence difference value that unequivocall y defined species boundaries. DNA-DNA hybridization remains the gold s tandard, but common resources are needed to permit DNA DNA hybridizati on analyses to be made available to laboratories that are not prepared to use this technology. One of the large novel clusters which we stud ied corresponds to the recently described species Mycobacterium interj ectum, a pathogen that resembles the nonpathogen Mycobacterium gordona e phenotypically. We also identified strains that appear to represent ribovars of Mycobacterium intracellulare which do not react with the c ommercial diagnostic probes that are currently used for identification of this species. Other branches or clusters consisted of too few stra ins to permit a decision about their taxonomic status to be made.