Numerical Classification of Some Named Strains of Nocardia asteroides and Related Isolates from Soil

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Abstract
Strains (149) of nocardiae, freshly isolated from soil samples obtained from a number of countries with either tropical or temperate climates, and from rubber pipe seals, were compared with appropriate marker cultures in a numerical phenetic study using 156 unit characters. Marker strains were chosen to represent the N. asteroides complex, other Nocardia spp. and related taxa, in an effort to classify the new soil isolates and, possibly, clarify the structure of the heterogeneous N. asteroides complex. The data were examined using the simple matching (SSM) and pattern (DP) coefficients, and clustering was achieved using both single and average linkage algorithms. Cluster composition was not markedly affected by either of the coefficients or clustering methods. The estimated test error of 7.1% was rather high and could account for a few apparently anomalous results. The 16 defined clusters, containing 185 of the 197 strains studied, were divided into 7 major and 9 minor clusters, 4 of which were further subdivided into 2 subclusters. Marker strains allowed 4 clusters to be designated as N. asteroides, 7 as Nocardia spp. and 1 each as N. carnea, N. farcinica, N. autotrophica, Mycobacterium farcinogenes and Rhodococcus spp. Twelve strains formed single member clusters, including the type strains of N. aerocolonigenes, N. amarae, N. fukuyae, N. orientalis and N. otitidis-caviarum. The majority of the soil and rubber isolates were recovered in the major clusters labeled N. asteroides, N. carnea and Nocardia spp. and clusters of soil isolates without marker strains seem to represent new centers of variation. The study highlights the need for additional reproducible tests to help both define and determine the status of defined clusters within the N. asteroides complex which would considerably benefit both the ecological and epidemiological study of these organisms.

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