Actinomyces

Background

Microbiology

• 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
• 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

Pulmonary Actinomycosis

• Presents as a chronic, non-resolving pneumonia or as a lung cancer
• Can spread directly to involve heart as well

Others

• Endocarditis
• Blood culture contamination1

Management

• First-line is penicillin IV x4-6 weeks then penicillin PO x6-12 months
• Alternatives include ceftriaxone, clindamycin, and doxycycline
• May need surgery

Further Reading

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