Introduction
- Actinomyces are Gram-positive, branching, filamentous bacteria that normally live in the mouth, gastrointestinal tract, and female genital tract.
- Although they are part of the normal human flora, they can cause disease when they enter deep tissues through injury or surgery.
- The infection caused by Actinomyces is known as actinomycosis.
- It is a chronic, slowly progressive bacterial infection characterized by abscess formation, fibrosis, and draining sinuses that may discharge yellow-colored granules called sulfur granules.
Classification
| Feature | Description |
|---|---|
| Kingdom | Bacteria |
| Phylum | Actinobacteria |
| Family | Actinomycetaceae |
| Genus | Actinomyces |
| Oxygen Requirement | Anaerobic or microaerophilic |
| Gram Stain | Gram-positive |
| Shape | Branching filamentous rods |
| Spore Formation | Non-spore forming |
Morphology
Actinomyces have unique microscopic features that resemble fungal hyphae.
Characteristics
- Gram-positive
- Thin, branching filamentous rods
- Non-spore forming
- Non-motile
- Anaerobic or microaerophilic
- Grow slowly in laboratory culture
Because they resemble fungal filaments, they were once considered fungi, but they are actually bacteria.
Habitat
Actinomyces are normal inhabitants of:
- Oral cavity
- Dental plaques
- Tonsillar crypts
- Gastrointestinal tract
- Female genital tract
They usually do not cause disease unless the protective mucosal barrier is damaged.
Epidemiology
- Worldwide distribution
- Rare infection
- More common in adults
- Males are affected more frequently than females
- Poor oral hygiene increases the risk
- Common in people with dental disease
Risk Factors
The following conditions increase the risk of actinomycosis:
- Poor oral hygiene
- Dental caries
- Tooth extraction
- Oral trauma
- Diabetes mellitus
- Immunosuppression
- Long-term intrauterine device (IUD) use
- Gastrointestinal surgery
- Aspiration
Mode of Transmission
Actinomycosis is not contagious.
The infection develops when normal bacteria enter deeper tissues through:
- Dental procedures
- Trauma
- Surgery
- Mucosal injury
- Aspiration of oral secretions
There is no person-to-person transmission.
Pathogenesis
| Step | Process | Description |
|---|---|---|
| 1 | Normal Flora | Actinomyces normally live harmlessly in the oral cavity, gastrointestinal tract, and female genital tract as part of the normal microbiota. |
| 2 | Mucosal Injury | Damage to the mucosal barrier due to tooth extraction, dental infection, trauma, surgery, foreign bodies, or aspiration allows the bacteria to enter deeper tissues. |
| 3 | Tissue Invasion | The bacteria invade deep tissues and multiply in low-oxygen (anaerobic) conditions, often with the help of other anaerobic bacteria. |
| 4 | Chronic Inflammation | A chronic suppurative (pus-forming) and granulomatous inflammatory response develops, leading to persistent infection. |
| 5 | Abscess Formation | Continuous bacterial growth and inflammation result in the formation of localized abscesses filled with pus. |
| 6 | Fibrosis and Sinus Tracts | Chronic infection causes fibrosis (scar tissue formation) and the development of draining sinus tracts that may open onto the skin or nearby tissues. |
| 7 | Sulfur Granules | The draining pus contains yellow sulfur granules, which are clusters of Actinomyces filaments surrounded by inflammatory cells. These granules are an important diagnostic feature. |
Clinical Manifestations
Actinomycosis can affect different parts of the body.
1. Cervicofacial Actinomycosis (Most Common)
Also called “Lumpy Jaw.”
Symptoms include:
- Swelling of jaw
- Pain
- Abscess formation
- Draining sinuses
- Sulfur granules in pus
Usually occurs after dental infection or tooth extraction.
2. Thoracic Actinomycosis
Occurs after aspiration.
Symptoms:
- Chronic cough
- Chest pain
- Fever
- Weight loss
- Lung abscess
3. Abdominal Actinomycosis
Usually follows bowel surgery or appendicitis.
Symptoms:
- Abdominal pain
- Fever
- Mass formation
- Abscess
4. Pelvic Actinomycosis
Associated with prolonged IUD use.
Symptoms:
- Pelvic pain
- Vaginal discharge
- Pelvic abscess
5. Central Nervous System Infection
Rare but serious.
May cause:
- Brain abscess
- Headache
- Seizures
- Neurological deficits
Laboratory Diagnosis
Diagnosis combines clinical findings with microbiological testing.
1. Specimen Collection
Common specimens include:
- Pus
- Tissue biopsy
- Aspirated abscess material
- Sinus discharge
Surface swabs are generally avoided because they may be contaminated with normal flora.
2. Direct Microscopy
Gram Staining
Findings:
- Gram-positive branching filamentous bacteria
- Sulfur granules may be present
Sulfur granules appear as yellow granules visible to the naked eye.
3. Histopathology
Microscopy may show:
- Sulfur granules
- Branching bacterial filaments
- Chronic inflammatory cells
- Fibrosis
4. Culture
Culture characteristics:
- Anaerobic incubation
- Slow growth (5–14 days)
- Small white colonies
- “Molar tooth” appearance on agar
5. Molecular Tests
Advanced laboratories may use:
- PCR
- 16S rRNA sequencing
- MALDI-TOF mass spectrometry
These methods provide rapid and accurate species identification.
Treatment
Actinomycosis responds well to antibiotics.
First-line treatment
- High-dose Penicillin G (intravenous)
Followed by:
- Oral Penicillin V
- Amoxicillin
Treatment usually continues for 6–12 months, depending on the severity and site of infection.
Alternative antibiotics (for penicillin allergy)
- Doxycycline
- Clindamycin
- Erythromycin
Surgical Management
Surgery may be required for:
- Drainage of abscesses
- Removal of necrotic tissue
- Excision of sinus tracts
- Large fibrotic masses
Prevention
Preventive measures include:
- Maintain good oral hygiene
- Regular dental check-ups
- Early treatment of dental infections
- Proper wound care
- Timely treatment of oral injuries
- Appropriate use and follow-up of intrauterine devices (IUDs)