Microbiology · MU Sofia

72. Genus Actinomyces.

Covers the general features of the genus Actinomyces: Gram-positive, branching filamentous bacilli that grow slowly and often need anaerobic conditions. It then sets out the pathogenic species, a table of virulence factors, and the pathogenesis of slow, invasive infection with sulfur granules. A section on clinical forms lists cervicofacial, thoracic, abdominal, pelvic and CNS actinomycosis, followed by diagnosis, penicillin-based treatment with alternatives, and prevention.

Inside: 9 sections · 5 labelled pictures · 1 table · 16 flashcards · 3 min

Topic 72 of 113 in the MU Sofia syllabus for Microbiology (Medicine, Year 3). The free AceMed note covers it in 9 sections, about 345 words (3 min of reading), with 16 flashcards.

In this note

  1. Genus Actinomyces
  2. General Characteristics
  3. Pathogenic Species
  4. Virulence Factors
  5. Pathogenesis
  6. Clinical Forms
  7. Diagnosis
  8. Treatment
  9. Prevention

General Characteristics

  • Gram-positive, non-spore-forming, non-acid-fast bacilli
  • Characteristic branching filamentous morphology (may resemble fungi microscopically)
  • Facultative or obligate anaerobes, grow best in reduced oxygen conditions
  • Very slow-growing, colonies may take 5–10 days to appear
  • Colonies on blood agar can appear “molar tooth” shaped
  • Part of normal human flora – especially in:
  • Oral cavity
  • Gastrointestinal tract
  • Female genital tract
  • Disease occurs after disruption of mucosal barriers (e.g., trauma, dental procedures, IUD)

Pathogenic Species

  • Actinomyces israelii – most common cause of human actinomycosis
  • A. gerencseriae , Propionibacterium propionicus,– other species with variable pathogenicity

Pathogenesis

  • Disease usually begins with mucosal damage (e.g., dental extraction, GI perforation, IUD use)
  • Organism invades deeper tissues → chronic inflammation
  • Forms suppurative granulomas, fibrosis, and multiple sinus tracts
  • Sulfur granules (yellow, firm granules in pus) are a hallmark
  • Spread is slow but invasive, can cross tissue planes and bones

Clinical Forms

  1. 1. Cervicofacial actinomycosis
  • Most common; "lumpy jaw"
  • Firm swelling in the jaw/neck area, discharging sinuses with sulfur granules
  • Often follows poor dental hygiene or oral surgery
  1. 2. Thoracic actinomycosis
  • Aspiration or contiguous spread
  • Presents with cough, chest pain, fever; can involve pleura and chest wall sinuses
  1. 3. Abdominal actinomycosis
  • Follows appendicitis, perforations, or surgery
  • Presents as abdominal mass, fever, bowel obstruction, or fistulas
  1. 4. Pelvic actinomycosis
  • Associated with intrauterine devices (IUD)
  • Mimics pelvic inflammatory disease or ovarian tumors
  1. 5. CNS actinomycosis (rare)
  • Brain abscess or chronic meningitis

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