[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Gram-positive rods](https://durgical.com/en/microbiology/groups/gram-positive-rods/) › Actinomyces israelii

[Microbiology](https://durgical.com/en/microbiology/) · [Gram-positive rods](https://durgical.com/en/microbiology/groups/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

## Key points

- Anaerobic, branching, not acid-fast.
- Sulfur granules and draining sinus tracts.
- Jaw after dental work; pelvis with an intrauterine device.
- Treated with prolonged penicillin.

## 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 →](https://durgical.com/en/conditions/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:

- [Benzylpenicillin (penicillin G)](https://durgical.com/en/pharmacology/benzylpenicillin/)

## Prevention

- Good dental hygiene and treatment of dental abscesses

## Memory aid

Actinomyces: A for anaerobe and for amber: golden grains leaking from sinus tracts in the jaw, and penicillin puts them out.

## 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).

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/microbiology/actinomyces-israelii/)

## Related

- [Nocardia](https://durgical.com/en/microbiology/nocardia/)

## Related conditions

- [Actinomycosis](https://durgical.com/en/conditions/actinomycosis/)

## What the colours mean

**Gram-positive**
Thick peptidoglycan wall: stains purple.

**Gram-negative**
Thin wall with an outer membrane: stains pink.

**Acid-fast**
Lipid-rich wall (mycobacteria): Ziehl–Neelsen stain.

[← Back to the group: Gram-positive rods](https://durgical.com/en/microbiology/groups/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](https://medlineplus.gov/ency/article/000599.htm) (MedlinePlus (NLM), 2024); [Pulmonary actinomycosis: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/000074.htm) (MedlinePlus (NLM), 2024).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/actinomyces-israelii/