A numerical analysis of 369 strains received as members of the genus Mycobacterium, Rhodococcus (formerly Gordona) , Nocardia, or Corynebacterium was carried out using 88 characters. Of the strains tested, 345 mycobacteria, rhodococci, and nocardiae formed four distinct clusters at a similarity level of 85%. The first cluster was composed of slowly growing mycobacteria; the second cluster, of strains of Mycobacterium flavescens and M. thermoresistibile; the third cluster, of strains of rapidly growing mycobacteria; and the fourth cluster, of strains of Rhodococcus and Nocardia. Strains of three species of rapidly growing mycobacteria, M. agri, M. smegmatis, and M. vaccae, were located outside of these clusters. The fourth cluster could be divided into three subclusters, one consisting of rhodococci plus some strains of Nocardia asteroides, a second consisting of the remaining strains of Nocardia, and a third consisting of strains of Rhodococcus aurantiacus (Gordona aurantiaca) and Jensenia canicruria.Mycobacterium, Rhodococcus (formerly Gordona), and Nocardia are closely related taxa belonging to the order Actinomycetales (21).In 1966, Tsukamura (13) reported that mycobacteria can be divided into two subgroups, which roughly correspond to slowly growing and rapidly growing mycobacteria, by numerical classification. These two subgroups differed from each other not only in growth rate, but also in several biological characters. Subsequently, Tsukamura and Mizuno (14, 24) proposed the subgeneric names Mycobacterium and Mycomycobacterium for these subgroups. Later, after having compared mycobacteria and nocardiae, Tsukamura (17) recommended that the subgenera Myco bacterium (slowly growing mycobacteria) and Mycomycobacterium (rapidly growing mycobacteria) be elevated to genus status, i.e., taxa equivalent in status to the genus Nocardia.In 1971, Tsukamura (18) proposed a new genus, Gordona, for slightly acid-fast organisms considered to be intermediate between Mycobacterium and Nocardia and placed it in the family Actinomycetaceae, to which the genus Nocardia belongs. It was later shown by Tsukamura that the genus Gordona contained strain ATCC 13808 of Rhodococcus rhodochrous (19), and it was stated that the generic name Gordona should be changed to Rhodococcus (20), as this is the first name used for an organism belonging to the genus proposed. Independently, Goodfellow (2) observed that "Mycobacterium" rhodochrous differs from nocardiae, and Goodfellow et al. (4) reported that it also differs from rapidly growing mycobacteria.The finding that "M. " rhodochrous differs from both Mycobacterium and Nocardia was conf m e d by an international cooperative study (5). Goodfellow and Alderson (3) also proposed the name Rhodococcus for the "M. " rhodochrous complex, in which they included the genus Gordona. These authors also included several new species in the genus Rhodococcus.The taxonomic relationships of the mycobacteria, rhodococci, and nocardiae were studied by Tsukamura (21), who included hypothetical median organi...

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We performed numerical analyses of 155 strains of rapidly growing, scotochromogenic mycobacteria by two different methods; in one method we used 104 characters, and in the other we used 84 characters. The following taxa appeared as distinct clusters: Myco bacterium thermoresistibile, Myco bacterium flavescens, Mycobacterium duvalii, Mycobacterium phlei, "Mycobacterium o buense," Myco bacterium parafortuitum, Mycobacterium vaccae, Mycobacterium sphagni, "Mycobacterium aichiense," "Mycobacterium rhodesiae," Mycobacterium neoaurum, "Mycobacterium chubuense," "Myco bacterium tokaiense," and Mycobacterzum komossense (names in quotation marks are not on the ApprovedLists of Bacterial Names). M. flavescens strains were divided into two subgroups, one consisting of strains isolated in Japan and the other consisting of strains isolated in Rhodesia and strains received from the American Type Culture Collection, including the type strain of M. flavescens (ATCC 14474). We found that there are many species of rapidly growing, scotochromogenic mycobacteria, and we believe that new species should be recognized and named on the basis of at least three strains. The following species appeared to be distinct from all presently named species: "Mycobacterium gallinarum," "Mycobacterium armentun," "Mycobacterium pelpallidurn," and "Mycobacterium taurus." However, each of these species was proposed on the basis of only one or two strains. Because of the small number of strains studied, formal proposals for these species should not be made until more strains of each taxon are studied. Furthermore, we consider "Myco bacterium magistrae" and "Myco bacterium auratum" to be synonyms of M. flavescens, "Mycobacterium pallidum" to be a synonym of M. parafortuitum, "Mycobacterium liquefactum" to be a synonym of M. vaccae, and "Mycobacterium sufflavum" to be a synonym of M. neoaurum. "M. obuense," "M. rhodesiae," "M. aichiense," "M. chubuense," and "M. tokaiense" are not on the Approved Lists of Bacterial Names, but based on the results of this study, we consider these organisms distinct species. Therefore, these names are revived for the same organisms with which they were originally associated. The type strains of these species are strain 47001 (=ATCC 27023 =NCTC 10778), strain 02002 (=ATCC 27024 -NCTC 10779), strain 49005 (=ATCC 27280 =NCTC 10820), strain 48013 (=ATCC 27278 =NCTC 10819), and strain 47503 (=ATCC 27282 =NCTC 10821), respectively. Mycobacterium flavescens

Type or representative strains of rapidly growing mycobacteria were tested in respect to 97 characters and submitted to a numerical classification. The results revealed that the following species be recognized: (1) Mycobacterium rhodochrous; (2) M. chitae; (a) M. phlei; (4) M. thamnopheos; (5) M. borstelense; (6) M. fortuitum; (7) M. vaccae; (8) M. parafortuitum; (9) M. smegmatis. Biologic and biochemical characters of type strains of these species were described. M. fortuitum was divided into two subspecies, M. fortuitum subsp. fortuitum and M. fortuitum subsp. abscessus. M. runyonii is synonym of M. abscessus and therefore has been included to the subspecies abscessus. M. parafortuitum was divided into two subspecies, M. parafortuitum subsp. parafortuitum and M. parafortuitum subsp. aurum, M. aurum being reduced to a subspecies. M. smegmatis was divided into two subspecies (or varieties), M. smegmatis subsp. smegmatis and M. smegmatis subsp. lacticola.