Actinomyces graevenitzii sp. nov., isolated from human clinical specimens.

Four strains of a previously unknown, catalase-negative, facultatively anaerobic, gram-positive, rod-shaped organism originating from humans were characterized by biochemical, chemical, and molecular taxonomic methods. The four strains phenotypically closely resembled one another, and although they possessed characteristics consistent with membership in the genus Actinomyces, they differed from all previously recognized species of this genus. The results of comparative 16S rRNA gene sequencing studies demonstrated that the unknown human bacterium was phylogenetically a member of the genus Actinomyces. Within the genus Actinomyces, the unidentified bacterium formed a loose, but statistically significant, association with a subgroup which included Actinomyces bovis, the type species of the genus. 16S rRNA sequence divergence values of > 6%, however, unequivocally demonstrated that the unidentified bacterium represents a new subline of the genus Actinomyces. A new species, Actinomyces graevenitzii, is proposed for the four new isolates. The type strain of A. graevenitzii is CCUG 27294.