Actinomyces Summary

Morphology and Physiology:

  Facultatively or strictly anaerobic Gram-positive bacilli (see WebLinked image)

  Bacteria with fungi-like structures:

  Form delicate filaments (often called hyphae or mycelia as per the structures formed by the true fungi) and aerial filaments which may branch, fragment into spores, or become pigmented
  Actinomyces actually means "ray fungus" in Greek
  Actinomyces are true bacteria due to the lack of mitochondria and a nuclear membrane, reproduction by cell fission and susceptibility to penicillin but not to antifungal chemotherapeutic agents

  Actinomyces are morphologically similar to Nocardia except that they Actinomyces are not acid-fast

  Grow slowly in culture and cause infections that are slow to develop and tend to be chronic

Epidemiology and Clinical Syndromes:

  Normal flora of the upper respiratory, gastronintestinal and femal genital tracts

  Low virulence potential, only causing opportunistic disease following disruption of mucosal barriers by trauma, surgery or infection


  May occur as acute pyogenic infection or more commonly as a chronic infection that is both suppurative and granulomatous
  Characterized by multiple abscesses and interconnecting sinus tracts that contain granules of microcolonies imbedded in tissue elements
  Microcolonies are macroscopic masses of filamentous bacterial cells that are "cemented" together by calcium phosphate
  Known as sulfur granules due to their yellow or orange appearance
  Chronic suppuration results in granuloma formation and a fibrotic "walling off" of the lesion 
  Ultimately resulting in bone involvement
  Five major clinical forms of actinomycoses based on site of infection:
      1. cervicofacial actinomycosis (most common form): associated with poor oral hygiene, an invasive dental procedure or oral trauma that is characterized by tissue swelling with fibrosis and draining sinus tracts along the jawline
      2. thoracic actinomycosis: associated with aspiration into the lungs and dissemination of the organisms into surrounding tissues
      3. abdominal actinomycosis: associated with abdominal surgery or intestinal trauma
      4. pelvic actinomycosis: primary infection associated with intrauterine devices in women and secondary infection associated with spread from abdominal actinomycosis
      5. cerebral actinomycosis: associated with secondary spread from another infected site and most commonly characterized by a single brain abscess

 Dental caries (see also Lactobacillus; Streptococcus mutans): associated with poor oral hygiene

 Periodontal disease: associated with poor oral hygiene

Laboratory Identification:

 Difficult to culture and identify because the numbers of organisms are limited in affected tissues and are sequestered in sulfur granules

 Fastidious and slow growth (up to two weeks or more)

 Colonies have "molar tooth" appearance on agar

Treatment and Prevention:

 Surgical debridement and long-term antibiotic therapy (susceptible to penicillin)

 Maintain good oral hygiene

 Prophylactic antibiotics prior to invasive oral or abdominal surgical procedures


   Go to Pathogen List



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