Microbiology · Gram-positive rods
Actinomyces israelii !
- Bacterium
- Gram-positive
- For completeness
A normal mouth bacterium that, after an injury, causes chronic abscesses with sinus tracts draining yellow grains, mostly in the jaw and neck.
Updated 2026-11-01
Also called: actinomycosis, lumpy jaw
At a glance
- Gram
- Gram-positive
- Shape
- Branching filaments
- Oxygen
- Anaerobe
- Family
- Actinomycetaceae
- Stain
- Gram positive; not acid-fast
Morphology
- Branching Gram-positive filaments
- Sulfur granules (yellow colonies) in the pus
- Not acid-fast
Transmission
- Endogenous flora of the mouth, gut and vagina (not contagious)
- Enters tissue after dental abscess, oral surgery or trauma
- Rare pelvic infection linked to an intrauterine device
Isolation precautions
What the care team adds to standard precautions.
- Standard
Virulence factors
- Invades tissue across anatomical planes
- Forms hard masses and chronic sinus tracts
Diseases it causes
- Cervicofacial, thoracic, abdominal and pelvic actinomycosis Actinomycosis →
Clinical picture
- A hard mass in the jaw or neck that opens into skin sinus tracts
- Can mimic a tumour
- Thoracic form after aspiration in people with poor dental hygiene
Diagnosis
- Sulfur granules in the pus
- Gram stain: branching filaments; slow anaerobic culture
- Tissue biopsy
Treatment
Prolonged penicillin (months), with surgical drainage or resection when needed; if linked to an intrauterine device, the device is removed.
Drug class only; doses and regimens are set by the clinician from the current guideline.
In Pharmacology:
Prevention
- Good dental hygiene and treatment of dental abscesses
Test yourself
Think of the answer, then tap the question to see it.
Which finding in pus suggests actinomycosis?
Sulfur granules: yellowish colonies of the bacterium.
How is actinomycosis treated?
Prolonged penicillin plus surgical drainage when needed.
Which device is linked to pelvic actinomycosis?
The intrauterine device (IUD).
Related
Related conditions
← Back to the group: Gram-positive rods
Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Actinomycosis: MedlinePlus Medical Encyclopedia (MedlinePlus (NLM), 2024); Pulmonary actinomycosis: MedlinePlus Medical Encyclopedia (MedlinePlus (NLM), 2024).
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Representative model, for educational purposes only.