1. A genus of slow-growing, nonmotile, nonsporeforming, anaerobic to facultatively anaerobic bacteria (family Actinomycetaceae) containing gram-positive, irregularly staining filaments; diphtheroid cells may be predominant. They exhibit true branching while forming mycelial-type colonies. Most of the species produce a filamentous microcolony. The metabolism of these chemoheterotrophs is fermentative; the products of glucose fermentation include acetic, formic, lactic, and succinic acids but not propionic acid. Actinomyces may have characteristic sulfur granules in purulent drainage. These organisms are pathogenic for humans and other animals and can cause chronic suppurative infection in humans. More than 16 species have been described; type species is Actinomyces bovis.
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