Classification

• Gram-positive
• Anaerobic (microaerophilic)
• Filamentous branching rods
• Part of normal oral, GI, and genital flora

Key Features

• Causes actinomycosis
• Chronic, slowly progressive infection
• Forms sulphur granules (yellow, gritty)
• Produces sinus tracts that drain pus
• Infection spreads across tissue planes (not lymphatics)

Common Sites

• Cervicofacial ("lumpy jaw") – most common
• Thoracic – aspiration risk
• Abdominal – post appendicitis or bowel perforation
• Pelvic – associated with long-term IUD use

Clinical Clues

• Hard, jaw mass after dental infection/extraction
• Draining sinus with yellow granules
• Chronic pelvic pain with IUD
• Chronic pulmonary mass mimicking malignancy

👉 Always think of actinomycosis when there is a chronic mass with sinus tracts + sulphur granules.

Diagnosis

• Anaerobic culture (slow growth)
• Microscopy → branching filamentous rods
• Histology → sulphur granules

Treatment

• High-dose Penicillin for weeks–months
• If allergic → doxycycline or macrolides
• Remove IUD if pelvic disease present
• Surgical drainage for abscesses

Differential (Actinomyces vs Nocardia)

Exam Pearls ✔

• Sulphur granules = Actinomyces
• Penicillin is DOC
• Pelvic actinomycosis linked to IUD
• Draining sinus tracts across tissues