Actinomyces

Background

Microbiology

• Genus of weakly Gram-positive branching bacillus that looks fungal under microscopy
• Molar tooth appearance of colonies
• Member of oral and gut flora
• Often part of polymicrobial infections involving other commensal flora
• Includes the following species of medical importance: Actinomyces israelii (most commone), Actinomyces gerencseriae, Actinomyces meyeri (more likely to disseminate), Actinomyces viscosus, Actinomyces naeslundii, Actinomyces odontolyticus, Actinomyces neuii, Actinomyces turicensis, Actinomyces radingae, Actinomyces pyogenes, Actinomyces georgiae, Actinomyces graevenitzii, Actinomyces propionica

Pathophysiology

• Spreads by direct invasion through tissue and creating fistulae

Clinical Manifestations

Cervicofacial Actinomycosis

• "Lumpy jaw syndrome" with painless jaw mass, trismus, and eventually pain
  • Starts as mass or cold abscess in neck, jaw, or mouth
  • Can invade bone
  • Spreads contiguously
• Often no systemic symptoms like fever
• May have "sulfur granules" discharge
• Most common form, accounting for ~50% of cases

Abdominal Actinomycosis

• Presents as an abdominal mass that fistulizes to skin
  • Organs affected can include appendix, cecum, colon, liver, biliary tract, pancreas, esophagus, rectum, and spleen
• Second most common presentation in about 25% of cases

Thoracic Actinomycosis

• Includes pulmonary, bronchial, and laryngeal actinomycosis
• Presents as a chronic, non-resolving pneumonia or as a lung cancer
• Can spread directly to involve heart as well
• Accounts for about 15% of cases

Pelvic Actinomycosis

• Less than 5% of cases
• Can involve uterus, fallopian tubes, ovaries, bladder, and kidneys

Others

• Soft tissue infections
• Bone and joint infections
• CNS infections
• Endocarditis
• Blood culture contamination1

Diagnosis

• Isolation of Actinomyces in culture from a sterile site
• Identification of sulfur granules with compatible clinical syndrome and/or histology

Management

• First-line is penicillin IV x4-6 weeks then penicillin PO x6-12 months
• Alternatives include ceftriaxone, clindamycin, and doxycycline
• May need surgery, including for abscess drainage, debridement, management of fistulas, etc.

Further Reading

• Actinomyces and Related Organisms in Human Infections. doi: https://doi.org/10.1128/CMR.00100-14