Actinomyces is a genus of the Actinomycetia class of bacteria. They all are Gram-positive and facultatively anaerobic, growing best under anaerobic conditions. The aspect of these colonies initially led to the incorrect assumption that the organism was a fungus and to the name Actinomyces, "ray fungus" (from Greek , ray or beam, and , fungus).

Actinomyces species are ubiquitous, occurring in soil and in the microbiota of animals, including the human microbiota. They are known for the important role they play in soil ecology; they produce a number of enzymes that help degrade organic plant material, lignin, and chitin. Thus, their presence is important in the formation of compost. Certain species are commensal in the skin flora, oral flora, gut flora, and vaginal flora of humans and livestock. They are also known for causing diseases in humans and livestock, usually when they opportunistically gain access to the body's interior through wounds. As with other opportunistic infections, people with immunodeficiency are at higher risk. In all of the preceding traits and in their branching filament formation, they bear similarities to Nocardia.

Like various other anaerobes, Actinomyces species are fastidious, thus not easy to culture and isolate. Clinical laboratories do culture and isolate them, but a negative result does not rule out infection, because it may be due simply to reluctance to grow in vitro.

Genomics

Phylogenetic trees based on 16S ribosomal RNA (16SrRNA) sequences have shown that the genus Actinomyces is quite diverse, exhibiting polyphyletic branching into several clusters. The genera Actinomyces and Mobiluncus form a monophyletic clade in a phylogenetic tree constructed using RpoB, RpoC, and DNA gyrase B protein sequences. This clade is also strongly supported by a conserved signature indel consisting of a three-amino-acid insertion in isoleucine tRNA synthetase found only in the species of the genera Actinomyces and Mobiluncus.

Pathology

Actinomycota are normally present in the gingiva, and are the most common cause of infection in dental procedures and oral abscesses. Many Actinomyces species are opportunistic pathogens of humans and other mammals, particularly in the oral cavity. In rare cases, these bacteria can cause actinomycosis, a disease characterized by the formation of abscesses in the mouth, lungs, or the gastrointestinal tract. Actinomycosis is most frequently caused by A. israelii, which may also cause endocarditis, though the resulting symptoms may be similar to those resulting from infections by other bacterial species.

The genus is typically the cause of oral-cervicofacial disease. It is characterized by a painless "lumpy jaw". Lymphadenopathy is uncommon in this form of the disease. Another form of actinomycosis is thoracic disease, which is often misdiagnosed as a neoplasm, as it forms a mass that extends to the chest wall. It arises from aspiration of organisms from the oropharynx. Symptoms include chest pain, fever, and weight loss. Abdominal disease is another manifestation of actinomycosis. This can lead to a sinus tract that drains to the abdominal wall or the perianal area. Symptoms include fever, abdominal pain, and weight loss. Actinomyces species have also been shown to infect the central nervous system in a dog "without history or evidence of previous trauma or other organ involvement."

Pelvic actinomycosis is a rare but proven complication of use of intrauterine devices. In extreme cases, pelvic abscesses might develop. Treatment of pelvic actinomycosis associated with intrauterine devices involves removal of the device and antibiotic treatment.

Diagnosis

Actinomycosis may be considered when a patient has chronic progression of disease across tissue planes that is mass-like at times, sinus tract development that may heal and recur, and refractory infection after a typical course of antibiotics. as well as surgery if the disease is extensive.

<!-- Actinomyces acrimycini was reclassified as Streptomyces griseus. -->

  • "A. actinomycetemcomitans" <small>Iinuma et al. 1994</small>

<!-- Actinomyces ahygroscopicus was reclassified as Streptomyces ahygroscopicus. -->

<!-- Actinomyces alboflavus was reclassified as Streptomyces alboflavus. -->

<!-- Actinomyces albosporeus was reclassified as Streptomyces aurantiacus. -->

<!-- Actinomyces albovinaceus was reclassified as Streptomyces globisporus. -->

<!-- Actinomyces alboviridis was reclassified as Streptomyces microflavus. -->

<!-- Actinomyces almquisti was reclassified as Streptomyces albus. -->

<!-- Actinomyces ansochromogenes was reclassified as Streptomyces ansochromogenes. -->

<!-- Actinomyces anthocyanicus was reclassified as Streptomyces anthocyanicus. -->

<!-- Actinomyces antibioticus was reclassified as Streptomyces antibioticus. -->

<!-- Actinomyces atroolivaceus was reclassified as Streptomyces atroolivaceus. -->

<!-- Actinomyces atrovirens was not included in the Approved Lists. -->

<!-- Actinomyces aurantiogriseus was reclassified as Streptomyces aurantiogriseus. -->

<!-- Actinomyces aureocirculatus was reclassified as Streptomyces aureocirculatus. -->

<!-- Actinomyces aureoverticillatus was reclassified as Streptomyces aureoverticillatus. -->

<!-- Actinomyces bacillaris was reclassified as Streptomyces bacillaris. -->

<!-- Actinomyces badius was reclassified as Streptomyces badius. -->

<!-- Actinomyces bernardiae was reclassified as Trueperella bernardiae. -->

<!-- Actinomyces biverticillatus was reclassified as Streptomyces hiroshimensis. -->

<!-- Actinomyces bobili was reclassified as Streptomyces bobili. -->

  • "A. bouchesdurhonensis" <small>Fonkou et al. 2018</small>
  • A. bovis <small>Harz 1877 (Approved Lists 1980)</small>
  • A. bowdenii <small>Pascual et al. 1999</small>

<!-- Actinomyces cacaoi was reclassified as Streptomyces cacaoi. -->

<!-- Actinomyces caeruleus was reclassified as Actinoalloteichus caeruleus. -->

<!-- Actinomyces californicus was reclassified as Streptomyces californicus. -->

<!-- Actinomyces canis was reclassified as Schaalia canis. -->

  • "A. capricornis" <small>Saito et al. 2021</small>

<!-- Actinomyces cardiffensis was reclassified as Schaalia cardiffensis . -->

  • A. catuli <small>Hoyles et al. 2001</small>

<!-- Actinomyces cellulosae was reclassified as Streptomyces cellulosae. -->

<!-- Actinomyces chromofuscus was reclassified as Streptomyces chromofuscus. -->

<!-- Actinomyces chryseus was reclassified as Streptomyces chryseus. -->

<!-- Actinomyces cinnabarinus was reclassified as Streptomyces cinnabarinus. -->

<!-- Actinomyces citreofluorescens was reclassified as Streptomyces anulatus. -->

<!-- Actinomyces clavifer was reclassified as Streptomyces clavifer. -->

<!-- Actinomyces coelescens was reclassified as Streptomyces anthocyanicus. -->

<!-- Actinomyces coeruleofuscus was reclassified as Streptomyces coeruleofuscus. -->

<!-- Actinomyces coeruleorubidus was reclassified as Streptomyces coeruleorubidus. -->

<!-- Actinomyces coerulescens was reclassified as Streptomyces coerulescens. -->

<!-- Actinomyces coleocanis was reclassified as Gleimia coleocanis. -->

<!-- Actinomyces cremeus was reclassified as Streptomyces cremeus. -->

  • "A. culturomici" <small>Fonkou et al. 2018</small>

<!-- Actinomyces cyaneofuscatus was reclassified as Streptomyces cyaneofuscatus. -->

<!-- Actinomyces cyaneus was reclassified as Streptomyces cyaneus. -->

<!-- Actinomyces cyanoalbus was reclassified as Streptomyces hirsutus. -->

<!-- Actinomyces daghestanicus was reclassified as Streptomyces daghestanicus. -->

  • A. dentalis <small>Hall et al. 2005</small>
  • A. denticolens <small>Dent and Williams 1984</small>

<!-- Actinomyces dentocariosus was reclassified as Rothia dentocariosa. -->

<!-- Actinomyces diastaticus was reclassified as Streptomyces diastaticus. -->

<!-- Actinomyces diastatochromogenes was reclassified as Streptomyces diastatochromogenes. -->

<!-- Actinomyces eriksonii was not included in the Approved Lists. -->

<!-- Actinomyces erythreus was reclassified as Saccharopolyspora erythraea. -->

<!-- Actinomyces europaeus was reclassified as Gleimia europaea. -->

<!-- Actinomyces exfoliatus was reclassified as Streptomyces exfoliatus. -->

  • A. faecalis <small>Zhou et al. 2021</small>

<!-- Actinomyces fimbriatus was reclassified as Streptomyces fimbriatus. -->

<!-- Actinomyces fimicarius was reclassified as Streptomyces griseus. -->

<!-- Actinomyces finlayi was reclassified as Streptomyces finlayi. -->

<!-- Actinomyces flaveolus was reclassified as Streptomyces flaveolus. -->

<!-- Actinomyces flavidovirens was reclassified as Streptomyces flavidovirens. -->

<!-- Actinomyces flavogriseus was reclassified as Streptomyces flavovirens. -->

<!-- Actinomyces flavotricini was reclassified as Streptomyces flavotricini. -->

<!-- Actinomyces flavovirens was reclassified as Streptomyces flavovirens. -->

<!-- Actinomyces flocculus was reclassified as Streptomyces albus. -->

<!-- Actinomyces fluorescens was reclassified as Streptomyces anulatus. -->

<!-- Actinomyces fradii was reclassified as Streptomyces fradiae. -->

<!-- Actinomyces fulvissimus was reclassified as Streptomyces microflavus. -->

<!-- Actinomyces fulvoviolaceus was reclassified as Streptomyces fulvoviolaceus. -->

<!-- Actinomyces fulvoviridis was reclassified as Streptomyces fulvoviridis. -->

<!-- Actinomyces fumanus was reclassified as Streptomyces fumanus. -->

<!-- Actinomyces funkei was reclassified as Schaalia funkei. -->

<!-- Actinomyces gallicus was reclassified as Micromonospora gallica. -->

  • A. gaoshouyii <small>Meng et al. 2017</small>

<!-- Actinomyces gelaticus was reclassified as Streptomyces gelaticus. -->

<!-- Actinomyces georgiae was reclassified as Schaalia georgiae. -->

  • A. gerencseriae <small>Johnson et al. 1990</small>

<!-- Actinomyces gibsonii was reclassified as Streptomyces albus. -->

<!-- Actinomyces glaucescens was reclassified as Streptomyces glaucescens. -->

<!-- Actinomyces globisporus was reclassified as Streptomyces globisporus. -->

<!-- Actinomyces globosus was reclassified as Streptomyces globosus. -->

<!-- Actinomyces glomeroaurantiacus was reclassified as Streptomyces aurantiacus. -->

  • "A. glycerinitolerans" <small>Palakawong Na Ayudthaya et al. 2016</small>

<!-- Actinomyces gobitricini was reclassified as Streptomyces gobitricini. -->

<!-- Actinomyces gougeroti was reclassified as Streptomyces diastaticus. -->

  • A. graevenitzii <small>Pascual Ramos et al. 1997</small>

<!-- Actinomyces griseoaurantiacus was reclassified as Streptomyces griseoaurantiacus. -->

<!-- Actinomyces griseoflavus was reclassified as Streptomyces griseoflavus. -->

<!-- Actinomyces griseoincarnatus was reclassified as Streptomyces griseoincarnatus. -->

<!-- Actinomyces griseoloalbus was reclassified as Streptomyces griseoloalbus. -->

<!-- Actinomyces griseolus was reclassified as Streptomyces halstedii. -->

<!-- Actinomyces griseomycini was reclassified as Streptomyces griseomycini. -->

<!-- Actinomyces griseorubens was reclassified as Streptomyces griseorubens. -->

<!-- Actinomyces griseorubiginosus was reclassified as Streptomyces griseorubiginosus. -->

<!-- Actinomyces griseostramineus was reclassified as Streptomyces griseostramineus. -->

<!-- Actinomyces griseus was reclassified as Streptomyces griseus. -->

  • A. haliotis <small>Hyun et al. 2014</small>

<!-- Actinomyces halstedii was reclassified as Streptomyces halstedii. -->

<!-- Actinomyces helvaticus was reclassified as Streptomyces helvaticus. -->

<!-- Actinomyces hominis was reclassified as Gleimia hominis. -->

<!-- Actinomyces hongkongensis was reclassified as Pauljensenia hongkongensis. -->

<!-- Actinomyces hordeovulneris was reclassified as Buchananella hordeovulneris. -->

  • "A. houstonensis" <small>Clarridge and Zhang 2002</small>
  • A. howellii <small>Dent and Williams 1984</small>

<!-- Actinomyces humiferus was reclassified as Cellulomonas humilata. -->

<!-- Actinomyces hygroscopicus was reclassified as Streptomyces hygroscopicus. -->

<!-- Actinomyces hyovaginalis was reclassified as Schaalia hyovaginalis. -->

  • "A. ihuae" <small>Fonkou et al. 2018</small>
  • "A. ihumii" <small>Ndongo et al. 2016</small>

<!-- Actinomyces ipomoea was reclassified as Streptomyces ipomoea. -->

  • A. israelii <small>(Kruse 1896) Lachner-Sandoval 1898 (Approved Lists 1980)</small>

<!-- Actinomyces janthinus was reclassified as Streptomyces janthinus. -->

  • A. johnsonii <small>Henssge et al. 2009</small>

<!-- Actinomyces kurssanovii was reclassified as Streptomyces kurssanovii. -->

<!-- Actinomyces lateritius was reclassified as Streptomyces lateritius. -->

<!-- Actinomyces lavendofoliae was reclassified as Streptomyces lavendofoliae. -->

<!-- Actinomyces lavendulae was reclassified as Streptomyces lavendulae. -->

<!-- Actinomyces lavendulocolor was reclassified as Streptomyces lavendulocolor. -->

<!-- Actinomyces levoris was not included in the Approved Lists. -->

  • A. lilanjuaniae <small>Li et al. 2019</small>
  • "A. lingnae" <small>Clarridge and Zhang 2002</small>

<!-- Actinomyces lipmanii was reclassified as Streptomyces microflavus. -->

<!-- Actinomyces litmocidini was reclassified as Streptomyces litmocidini. -->

<!-- Actinomyces liubingyangii was reclassified as Boudabousia liubingyangii. -->

<!-- Actinomyces longisporus was reclassified as Streptomyces longisporus. -->

<!-- Actinomyces luridus was reclassified as Streptomyces luridus. -->

<!-- Actinomyces malachitospinus was not included in the Approved Lists. -->

<!-- Actinomyces marimammalium was reclassified as Boudabousia marimammalium. -->

  • A. marmotae <small>Yang et al. 2021</small>
  • "A. marseillensis" <small>Fonkou et al. 2018</small>
  • A. massiliensis <small>Renvoise et al. 2009</small>
  • "A. mediterranea" <small>Fonkou et al. 2018</small>

<!-- Actinomyces meyeri was reclassified as Schaalia meyeri. -->

<!-- Actinomyces microflavus was reclassified as Streptomyces microflavus. -->

  • "A. minihominis" <small>Bilen et al. 2018</small>

<!-- Actinomyces mutabilis was reclassified as Streptomyces mutabilis. -->

<!-- Actinomyces naeslundi is a misspelling of Actinomyces naeslundii. -->

  • A. naeslundii <small>corrig. Thompson and Lovestedt 1951 (Approved Lists 1980)</small>

<!-- Actinomyces nasicola was reclassified as Bowdeniella nasicola. -->

<!-- Actinomyces naturae was reclassified as Schaalia naturae. -->

<!-- Actinomyces neuii was reclassified as Winkia neuii. -->

<!-- Actinomyces nigrescens was reclassified as Streptomyces nigrescens. -->

<!-- Actinomyces odontolyticus was reclassified as Schaalia odontolytica. -->

<!-- Actinomyces olivaceoviridis was reclassified as Streptomyces olivaceoviridis. -->

<!-- Actinomyces olivaceus was reclassified as Streptomyces olivaceus. -->

<!-- Actinomyces olivochromogenus was reclassified as Streptomyces olivochromogenus. -->

<!-- Actinomyces olivoviridis was reclassified as Streptomyces atroolivaceus. -->

  • "A. oralis" <small>Fonkou et al. 2018</small>
  • A. oricola <small>Hall et al. 2003</small>
  • A. oris <small>Henssge et al. 2009</small>
  • "A. pacaensis" <small>Fonkou et al. 2018</small>

<!-- Actinomyces parvus was reclassified as Streptomyces parvus. -->

<!-- Actinomyces pheochromogenus was reclassified as Streptomyces phaeochromogenus. -->

  • "A. polynesiensis" <small>Cimmino et al. 2016</small>

<!-- Actinomyces praecox was reclassified as Streptomyces anulatus. -->

  • A. procaprae <small>Yang et al. 2021</small>

<!-- Actinomyces propionicus was reclassified as Arachnia propionica. -->

  • "A. provencensis" <small>Ndongo et al. 2017</small>

<!-- Actinomyces prunicolor was reclassified as Streptomyces prunicolor. -->

<!-- Actinomyces pseudovenezuelae was reclassified as Streptomyces pseudovenezuelae. -->

<!-- Actinomyces purpeochromogenus was reclassified as Micromonospora purpureochromogenes. -->

<!-- Actinomyces pyogenes was reclassified as Trueperella pyogenes. -->

  • A. qiguomingii <small>Zhu et al. 2020</small>
  • A. radicidentis <small>Collins et al. 2001</small>

<!-- Actinomyces radingae was reclassified as Schaalia radingae. -->

<!-- Actinomyces rangoon was reclassified as Streptomyces albus. -->

<!-- Actinomyces rectiverticillatus was reclassified as Streptomyces hiroshimensis. -->

  • A. respiraculi <small>Zhou et al. 2021</small>

<!-- Actinomyces robefuscus was reclassified as Streptomyces robefuscus. -->

<!-- Actinomyces roseodiastaticus was reclassified as Streptomyces tricolor. -->

<!-- Actinomyces roseofulvus was reclassified as Streptomyces roseofulvus. -->

<!-- Actinomyces roseolilacinus was reclassified as Streptomyces roseolilacinus. -->

<!-- Actinomyces roseolus was reclassified as Streptomyces roseolus. -->

<!-- Actinomyces roseoviolaceus was reclassified as Streptomyces roseoviolaceus. -->

<!-- Actinomyces roseoviridis was reclassified as Streptomyces roseoviridis. -->

<!-- Actinomyces rubiginosohelvolus was reclassified as Streptomyces rubiginosohelvolus. -->

<!-- Actinomyces rubiginosus was reclassified as Streptomyces rubiginosus. -->

  • A. ruminicola <small>An et al. 2006</small>

<!-- Actinomyces rutgersensis was reclassified as Streptomyces diastaticus. -->

<!-- Actinomyces sampsonii was reclassified as Streptomyces albidoflavus. -->

<!-- Actinomyces setonii was reclassified as Streptomyces griseus. -->

  • A. slackii <small>Dent and Williams 1986</small>
  • "A. succiniciruminis" <small>Palakawong Na Ayudthaya et al. 2016</small>

<!-- Actinomyces suimastitidis was reclassified as Schaalia suimastitidis. -->

<!-- Actinomyces suis was reclassified as Actinobaculum suis. -->

<!-- Actinomyces sulphureus was reclassified as Streptomyces sulphureus. -->

<!-- Actinomyces tangfeifanii was reclassified as Boudabousia tangfeifanii. -->

<!-- Actinomyces thermodiastaticus was reclassified as Streptomyces thermodiastaticus. -->

  • A. timonensis <small>Renvoise et al. 2010</small>

<!-- Actinomyces toxytricini was reclassified as Streptomyces toxytricini. -->

  • A. trachealis <small>Zhou et al. 2021</small>

<!-- Actinomyces tricolor was reclassified as Streptomyces tricolor. -->

<!-- Actinomyces tumemacerans was not included in the Approved Lists. -->

<!-- Actinomyces turicensis was reclassified as Schaalia turicensis. -->

<!-- Actinomyces umbrinus was reclassified as Streptomyces umbrinus. -->

  • "A. urinae" <small>Morand et al. 2016</small>
  • A. urogenitalis <small>Nikolaitchouk et al. 2000</small>

<!-- Actinomyces vaccimaxillae was reclassified as Schaalia vaccimaxillae. -->

<!-- Actinomyces variabilis was reclassified as Streptomyces griseoincarnatus. -->

<!-- Actinomyces violaceochromogenes was reclassified as Streptomyces violaceochromogenes. -->

<!-- Actinomyces violaceolatus was reclassified as Streptomyces anthocyanicus. -->

<!-- Actinomyces violaceorectus was reclassified as Streptomyces violaceorectus. -->

<!-- Actinomyces violaceusniger was reclassified as Streptomyces violaceusniger. -->

<!-- Actinomyces violaceusruber was reclassified as Streptomyces violaceusruber. -->

<!-- Actinomyces violarus was reclassified as Streptomyces violarus. -->

<!-- Actinomyces violascens was reclassified as Streptomyces violascens. -->

<!-- Actinomyces violatus was reclassified as Streptomyces violaceus. -->

<!-- Actinomyces viridiviolaceus was reclassified as Streptomyces viridiviolaceus. -->

<!-- Actinomyces viridochromogenes was reclassified as Streptomyces viridochromogenes. -->

<!-- Actinomyces viridodiastaticus was reclassified as Streptomyces albogriseolus. -->

  • A. viscosus <small>(Howell et al. 1965) Georg et al. 1969 (Approved Lists 1980)</small>

<!-- Actinomyces vulgaris was not included in the Approved Lists. -->

  • A. vulturis <small>Meng et al. 2017</small>
  • A. weissii <small>Hijazin et al. 2012</small>

<!-- Actinomyces willmorei was reclassified as Streptomyces microflavus. -->

  • A. wuliandei <small>Zhu et al. 2020</small>

<!-- Actinomyces xantholiticus was reclassified as Streptomyces xantholiticus. -->

<gallery mode="packed" widths="360px" heights="220">

Image:Actinomyces - high mag.jpg|Micrograph of actinomycosis, H&E stain

Image:Actinomycosis GROCOTT'S.JPG|Micrograph of actinomycosis, GMS stain

Image:Actinomycosis GRAM'S.JPG|Micrograph of actinomycosis, Gram stain

</gallery>

References

  • Actinomyces naeslundii MG1 Genome Page
  • Actinomyces at BacDive - the Bacterial Diversity Metadatabase

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