Conventional identification of Nocardia in the routine laboratory remains problematic due to a paucity of reliable phenotypic tests and due to the yet-unresolved taxonomy of strains classified as belonging to the species Nocardia asteroides, which comprises the type strain and isolates with drug pattern types II and VI. The 16S rRNA gene of 74 representative strains of the genus Nocardia, encompassing 25 established species, was sequenced in order to provide a molecular basis for accurate species identification and with the aim of reassessing the phylogeny of taxons assigned to the species N. asteroides. The result of this phylogenetic analysis confirms that the interspecies heterogeneity of closely related nocardial species can be considerably low (a sequence divergence of only 0.5% was found between N. paucivorans and N. brevicatena). We observed a sequence microheterogeneity (sequence divergence of fewer than five bases) in 8 of 11 species of which more than one strain in the species was studied. At least 10 taxons were found that merit description as new species. Strains previously classified as N. asteroides fell into five distinct phylogenetic groups: the type strain cluster (N. asteroides sensu strictu), N. abscessus, N. cyriacigeorgica, and two clusters closely related to N. carnea or N. flavorosea. The strains within the latter two groups probably represent new species, pending further genetic and phenotypic evaluation. Restricted phenotypic data revealed that N. abscessus, N. cyriacigeorgica, and the two Nocardia species taxons are equivalent to drug patterns I, VI, and II, respectively. In the future, these data will help in finding species-specific markers after adoption of a more precise nomenclature for isolates closely related to N. asteroides and unravel confusing phenotypic data obtained in the past for unresolved groups of strains that definitely belong to separate taxons from a phylogenetic point of view.The genus Nocardia forms a group of 30 validly described species. Many of these can cause clinical diseases in humans and animals, including pulmonary, central nervous system, and cutaneous infections that are all diagnosed by culture and identification of the organisms (1, 10, 11). Identification to the genus level is well established based on chemotaxonomic characteristics, mainly on the presence of a major amount of mesodiaminopimelic acid, arabinose, galactose, and mycolic acids with 46 to 60 carbons in cell walls (13,14). A variety of phenotypic characteristics for each Nocardia species can be found in the literature, but those of recently published species, such as N. abscessus and N. cyriacigeorgica (25, 26), have not been analyzed in collaborative numerical phenetic studies systematically in order to obtain a proposal of selected tests for routine identification of all medically relevant species (9,13,17,19,21). Studies of antimicrobial susceptibility revealed distinct drug pattern types within strains identified as N. asteroides, notably drug patterns I through VI (20). A few years la...

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Comparative 16S rDNA studies of Nocardia type and reference strains revealed that strain DSM 43406 T , identified as Nocardia vaccinii, was wrongly classified. The strain was aerobic, Gram-positive and produced scarce, white, branched aerial mycelium and a beige-red substrate mycelium. The reverse side of the colonies was yellow-orange. It showed chemotaxonomic markers that were consistent with its classification in the genus Nocardia. The mycolic acids had chain lengths from 50 to 58 carbon atoms. The 16S rDNA sequence showed the highest similarity to Nocardia nova (977 %) and N. vaccinii (976 %), but the strain could be clearly separated from these species and other members of the N. vaccinii cluster by significant differences in biochemical test results and unique fatty acid and mycolic acid patterns. These data led to the conclusion that the isolate represents a novel species within the genus Nocardia, for which the name Nocardia pseudovaccinii sp. nov. is proposed. The type strain is strain AR 368,38366-20Keywords : Nocardia pseudovaccinii sp. nov., polyphasic taxonomyNocardiae are distributed ubiquitously in the environment and they are common in soil (Orchard et al., 1977 ;Wang et al., 2001). They are frequently isolated from rivers (Maldonado et al., 2000) and scumming activated sludge (Lemmer & Kroppenstedt, 1984). However, despite their essentially saprophytic nature, most attention has been focused on the taxonomy of clinically significant nocardiae. Most of the validly described Nocardia species have been isolated from humans and animals, where they cause a variety of suppurative diseases, notably actinomycete mycetoma (Schaal, 1972 ;Schaal & Lee, 1992) and pulmonary infections (Gu$ rtler et al., 2001 ;Hamid et al., 2001) and nocardiosis in fish (Kudo et al., 1988 ;Isik et al., 1999) and oysters (Friedman et al., 1998), or they produce stem galls on blueberry (Demaree & Smith, 1952