Actinomyces

Abstract Ac.ti.no.my'ces. Gr. fem. n. aktis, aktinos ray; Gr. masc. n. mukês fungus; N.L. masc. n. Actinomyces ray fungus referring to the radial arrangement of filaments in Actinomyces bovis sulfur granules. Straight or slightly curved rods , 0.2–1.0 µm in diameter, which vary considerably in shape and size, and slender filaments , 1 µm or less in width and 10–50 µm or more in length, with true branching. Short rods (0.5–5.0 µm in length) with or without clubbed ends are frequently seen and may occur singly, in pairs with diphtheroidal arrangements (Y, V, T forms and palisades), in short chains or in small clusters. Longer (5.0–10.0 µm in length) branched rods are also common. Several members of the genus appear chiefly or exclusively as coccobacillary or even coccoid elements. Filaments which may predominate in certain species are either straight or wavy , show varying degrees of branching and may have swollen, clubbed, or clavate ends. Gram‐stain‐positive , but irregular staining giving rise to a beaded or barred appearance frequently occurs, and two species may be Gram‐stain‐variable. Non‐acid‐fast, nonmotile, and non‐endospore‐forming. Conidia are not produced. DNA G+C content (mol%) : 55–71 ( T m , HPLC). Type species : Actinomyces bovis Harz 1877, 133 AL . Taxonomic and Nomenclature Notes According to the List of Prokaryotic names with Standing in Nomenclature (LPSN), the taxonomic status of the genus Actinomyces is: correct name (last update, February 2025) * . LPSN classification: Bacteria / Bacillati / Actinomycetota / Actinomycetes / Actinomycetales / Actinomycetaceae / Actinomyces The genus Actinomyces can also be recovered in the Genome Taxonomy Database (GTDB) as g__Actinomyces (version v220) ** . GTDB classification: d__Bacteria / p__Actinomycetota / c__Actinomycetes / o__Actinomycetales / f__Actinomycetaceae / g__Actinomyces * Meier‐Kolthoff et al. ( 2022 ). Nucleic Acids Res , 50 , D801 – D807 ; DOI: 10.1093/nar/gkab902 ** Parks et al. ( 2022 ). Nucleic Acids Res , 50 , D785 – D794 ; DOI: 10.1093/nar/gkab776