Nocardia pseudobrasiliensis sp. nov., a new species of Nocardia which groups bacterial strains previously identified as Nocardia brasiliensis and associated with invasive diseases.

We studied five strains of a new Nocardia taxon recently identified among Nocardia brasiliensis strains associated with invasive diseases (R. J. Wallace, Jr., B. A. Brown, Z. Blacklock, R. Ulrich, K. Jost, J. M. Brown, M. M. McNeil, G. Onyi, V. A. Steingrube, and J. Gibson, J. Clin. Microbiol. 33:1528-1533, 1995) to determine their taxonomic status. Several characteristics of these organisms, including the presence of chemotype IV cell walls, nocardomycolic acids, a predominant menaquinone similar to that of Nocardia asteroides ATCC 19247T (T = type strain), and G+C contents ranging from 67 to 68 mol%, are characteristics of the genus Nocardia. Phylogenies based on small-subunit ribosomal DNA sequences clearly confirmed that all five strains belong to the genus Nocardia and occur on a single branch that is clearly distinct from N. brasiliensis. This branch forms a clade with Nocardia vaccinii, Nocardia nova, Nocardia otitidiscaviarum, and Nocardia seriolae. The five new strains exhibited high levels of DNA relatedness with each other, as determined by DNA-DNA hybridization experiments (S1 nuclease procedure), but not with N. brasiliensis strains or with strains of the four phylogenetically related Nocardia species mentioned above. The five new strains differ from N. brasiliensis in the following characteristics: mycolic acid pattern, decomposition of adenine, nitrate reduction, and antimicrobial agent susceptibilities. Therefore, we propose that these strains belong to a new species, Nocardia pseudobrasiliensis. The type strain is strain ATCC 51512, which was isolated from a leg abscess on a patient suffering from ulcerative colitis.