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 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 reference laboratory strain H37Rv and clinical isolates of and . Furthermore, the So93 isolate differed from all complex strains described thus far by having only a single copy of insertion sequence IS, 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 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 complex taxa, , and . 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 complex and the newly described Canetti grouping should be regarded as a single species, which likely will be designated “”.


Article metrics loading...

Loading full text...

Full text loading...


Most cited this month Most Cited RSS feed

This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error