- General characteristics:
- Structure: branching, filamentous rods/bacilli
- Gram stain: gram-positive
- Other stain(s): not acid-fast
- Spore formation: non-spore–forming (differentiates Actinomyces from fungi)
- Oxygen requirement: anaerobe
- Culture medium: same as for other anaerobes
- Actinomycosis (disease-caused):
- Chronic suppurative and granulomatous infection
- Associated with abscess formation with interconnecting sinus tracts
- Sulfur granules:
- Characteristic finding
- Microcolonies of the bacteria with yellow color (no sulfur) and peripheral clubs
- Found embedded in tissue elements
Clinically relevant species
- A. israelii (most common)
- A. gerencseriae
- A. naeslundii
- A. viscosus
- A. odontolyticus
- A. meyeri
- Men > women
- Higher prevalence in low socioeconomic areas and in those with poor dental hygiene
- Use of intrauterine device (IUD) has increased incidence in women.
Reservoir and transmission
- Normal flora of:
- Oral cavity
- Reproductive tract
- Gastrointestinal (GI) tract
- Trauma displaces the organism.
- Breaching the mucosal barrier and moving to areas with low oxygen (anaerobic environment) facilitate its multiplication.
- Poor oral hygiene
- Dental surgery
- Dental trauma
- IUD use
- Malignancy and related local tissue damage (from the disease or from radiation treatment)
- Osteonecrosis of the jaw due to bisphosphonates
- The bacteria take advantage of the mucosal break, invading neighboring tissues.
- Once Actinomyces infection is established, inflammatory response follows (suppurative and granulomatous).
- Infection spreads by creating sinuses that contain sulfur granules; these may drain into the surface.
- Infections occur near the usual reservoir.
- Pulmonary infections occur, from direct extension of the oropharyngeal source or by aspiration of oral and GI secretions.
- Most common presentation
- Oral/facial abscesses in the jaw (“lumpy jaw”), draining through sinus tracts
- Commonly affects the maxilla, cheek, and lower jaw
- Forms characteristic yellow sulfur granules in pus or tissues:
- Resemble grains of sand
- Bacterial microcolonies
- May extend to other tissues, bones, and lymph nodes
- Trismus and difficulty chewing
- Pain occurs with compression of neighboring structures.
- Often associated with dental caries, extractions, or jaw trauma
- Aspiration of oropharyngeal secretions
- Introduction of bacteria via esophageal injury
- Direct extension from neck or abdomen
- Hematogenous spread
- Presents as subacute pulmonary infection: fever, cough with sputum
- Lung parenchyma: may have cavitations, which can form sinus tracts
- These tracts can go through the chest wall or invade the ribs.
- From a ruptured appendix/bowel or an ulcer
- Patient may have had prior abdominal surgery.
- Presents with fever, change in bowel habits, abdominal pain, weight loss
- Extension can affect any intraabdominal organ.
- In patients with an IUD
- May present as lower abdominal pain and vaginal discharge
- May cause pelvic abscesses
Diagnosis and Management
- Culture media and techniques: same as for other anaerobes
- Prolonged incubation (sometimes takes 7–21 days to appear)
- Pus (from draining sinuses)
- Specimens of tissue (with yellow-orange, microscopic sulfur granules)
- In some cases, Actinomyces is seen on Pap smear.
- If symptomatic of infection: IUD is removed and sent for culture.
- If without symptoms: Patient is educated on symptoms to watch for and IUD is left in place.
- Microscopic examination of sulfur granule: composed of tissue elements and branching actinomycotic filaments (club-shaped at the periphery)
- Imaging studies:
- Computed tomography (CT) scan of the abdomen: shows site and extent of the disease in abdominal infection
- CT of the chest:
- Evaluates thoracic infection
- Shows mass with central areas of low attenuation and ring-like rim enhancement
- Cavities also may be seen.
- Pelvic ultrasound:
- Obtained when patients present with symptoms of pelvic inflammatory disease
- Look for abscess
- Prolonged penicillin treatment
- Mild disease: 2–6 months
- Severe disease: 6–12 months
- Alternatives for penicillin-allergic patients: clindamycin or erythromycin
- Surgical incision and drainage may be required.
- Removal of IUD
Two clinically relevant gram-positive, branching, filamentous rods that must be distinguished:
|Acid-fast stain||Not acid-fast||Acid-fast (partially)|
|Reservoir/habitat||Normal oral, GI, and reproductive flora||Found in soil, water, decaying organic matter|
SNAP (Sulfonamides-Nocardia, Actinomyces–Penicillin)
- Appendicitis: presents with abdominal pain and tenderness, mostly in the right lower quadrant. Computed tomography scan can help diagnose appendicitis. Abdominal actinomycosis can occur if appendicitis is complicated with rupture.
- Odontogenic abscess/infection: arises after dental extraction or from an infected tooth. Infections are often polymicrobial; most common bacteria are Streptococcus viridians, Peptostreptococcus, and Staphylococcus. Culture will differentiate the organisms.
- Pelvic inflammatory disease: the more common bacteria involved in this disease are Chlamydia trachomatis and Neisseria gonorrhoeae. Infections from both organisms are sexually transmitted. Actinomycosis is often associated with IUD use.
- Riedel S, Hobden JA, et al (Eds.) (2019). Infections caused by anaerobic bacteria. In Jawetz, Melnick, & Adelberg’s Medical Microbiology (28th ed.) McGraw-Hill.
- Russo TA. (2018). Actinomycosis. In Jameson J, Fauci AS, et al (Eds.), Harrison’s Principles of Internal Medicine (20th ed.) McGraw-Hill.
- Ryan KJ (Ed.) (2017). Actinomyces and nocardia. In Sherris Medical Microbiology (7th ed.) McGraw-Hill.
- Sharma S, Hashmi M, Valentino D. (2020). Actinomycosis. StatPearls. Retrieved Nov 25, 2020, from https://www.ncbi.nlm.nih.gov/books/NBK482151/
- Valour F, Sénéchal A, et al (2014). Actinomycosis: etiology, clinical features, diagnosis, treatment, and management. Infect Drug Resist, 7, 183–197. https://dx.doi.org/10.2147%2FIDR.S39601