We studied the taxonomic interrelationships of 332 strains by using a numerical analysis that was based on 46 cultural and biochemical characters and involved both a hierarchical clustering procedure and a principal components analysis. and were recognized as relatively distinct phenotypic clusters. was further distinguishable from the remaining taxa by antigenic and enterotoxigenic parameters. These results supported the suggestion that deserves species status. On the other hand, sensu stricto, , and constituted a phenotypic continuum. Each of these three taxa prevailed in different parts of a heterogeneous cluster of strains that were connected by intermediate phenotypes. This pattern of overlapping phenotypes was supported further by antigenic properties, habitat preferences, and pathogenic characteristics. Thus, we failed to find a basis for separating sensu stricto, , and on phenetic, ecological, or pathogenic grounds. We suggest that the taxonomic relationships among these nomenspecies may require further evaluation. Two phenetic clusters contained strains not ascribable to any presently defined species. One of these clusters consisted mainly of rhamnose-positive, sucose-negative strains and the other contained strains negative for sucrose or ornithine decarboxylase or both.


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