Actinomyces/Actinomycosis

General Characteristics

Actinomyces

• 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

Epidemiology

• 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.

Pathogenesis

Reservoir and transmission

Reservoir:

• Normal flora of:
  • Oral cavity
  • Reproductive tract
  • Gastrointestinal (GI) tract

Transmission:

• Trauma displaces the organism.
• Breaching the mucosal barrier and moving to areas with low oxygen (anaerobic environment) facilitate its multiplication.

Risk factors

• Poor oral hygiene 
• Gingivitis
• Dental surgery
• Dental trauma
• IUD use
• Alcoholism
• Malnutrition
• Malignancy and related local tissue damage (from the disease or from radiation treatment)
• Diabetes
• Osteonecrosis of the jaw due to bisphosphonates

Pathophysiology

• 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.

Clinical Presentation

Cervicofacial disease

• 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
• Manifestations:
  • Trismus and difficulty chewing
  • Pain occurs with compression of neighboring structures.
• Often associated with dental caries, extractions, or jaw trauma

Thoracic actinomycosis

• Transmission: 
  • 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.

Abdominal actinomycosis

• 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.

Pelvic actinomycosis

• In patients with an IUD
• May present as lower abdominal pain and vaginal discharge
• May cause pelvic abscesses

Diagnosis and Management

Diagnosis

• Culture: 
  • Culture media and techniques: same as for other anaerobes 
  • Prolonged incubation (sometimes takes 7–21 days to appear)
  • Specimen(s): 
    • Pus (from draining sinuses)
    • Sputum
    • 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

Management

• 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 

Comparison

Two clinically relevant gram-positive, branching, filamentous rods that must be distinguished:

Mnemonic:

 SNAP (Sulfonamides-Nocardia, Actinomyces–Penicillin)

Differential Diagnosis

• 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.