RT Journal Article SR Electronic(1) A1 Van Soolingen, Dick A1 Hoogenboezem, Theo A1 De Haas, Petra E. W. A1 Hermans, Peter W. M. A1 Koedam, Marianne A. A1 Teppema, Koos S. A1 Brennan, Patrick J. A1 Besra, Gurdyal S. A1 Portaels, Francoise A1 Top, Janetta A1 Schouls, Leo M. A1 Van Embden, Jan D. A.YR 1997 T1 A Novel Pathogenic Taxon of the Mycobacterium tuberculosis Complex, Canetti: Characterization of an Exceptional Isolate from Africa JF International Journal of Systematic and Evolutionary Microbiology, VO 47 IS 4 SP 1236 OP 1245 DO https://doi.org/10.1099/00207713-47-4-1236 PB Microbiology Society, SN 1466-5034, AB In an attempt to characterize an unusual mycobacterial strain isolated from a 2-year-old Somali patient with lymphadenitis, we applied various molecular methods not previously used for the taxonomic classification of mycobacteria. This isolate, designated So93, did not differ from Mycobacterium tuberculosis in the biochemical tests and in its 16S rRNA sequence, but produced smooth and glossy colonies, which is highly exceptional for this species. This smooth phenotype was unstable and switched nonreversibly to a rough colony morphology with a low frequency. The two colony types were equally virulent for the guinea pig, exhibiting characteristic tuberculous disease. Both morphotypes had shorter generation times than the M. tuberculosis reference laboratory strain H37Rv and clinical isolates of M. tuberculosis and Mycobacterium bovis. Furthermore, the So93 isolate differed from all M. tuberculosis complex strains described thus far by having only a single copy of insertion sequence IS1081, an unusual composition of the direct repeat cluster, and a characteristic phenolic glycolipid and lipooligosaccharide. This glycolipid had previously been observed only in a smooth isolate of M. tuberculosis obtained in 1969 by Canetti in France. Analysis of the Canetti strain showed that it shared virtually all genetic properties characteristic of So93, distinguishing these two strains from the known M. tuberculosis complex taxa, M. tuberculosis, Mycobacterium africanum, M. bovis, and Mycobacterium microti. The natural reservoir, host range, and mode of transmission of the group of bacteria described in this paper are presently unknown. This study, partly based on not previously used molecular criteria, supports the idea that the established members within the M. tuberculosis complex and the newly described Canetti grouping should be regarded as a single species, which likely will be designated “M. tuberculosis”., UL https://www.microbiologyresearch.org/content/journal/ijsem/10.1099/00207713-47-4-1236