Skin nontumor
Infectious disorders

Topic Completed: 1 November 2015

Minor changes: 17 August 2020

Copyright: 2003-2020,, Inc.

PubMed Search: Actinomycosis [title] skin

Abha Soni, D.O., M.P.H.
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Cite this page: Soni A, Slominski A. Actinomycosis. website. Accessed October 21st, 2020.
Definition / general
  • Most common causative agent is Actinomyces israelii
  • "Sulfur granules": small yellow granules found within the abscesses formed by Actinomyces infection (Ophthal Plast Reconstr Surg 1992;8:237)
  • "Lumpy jaw syndrome": large abscesses located on the head and neck, usually following dental disease and mandibular osteomyelitis (BMJ Case Rep 2015 Feb 5;2015)
  • Cervicofacial (post dental infection), skin (post traumatic injury creating an anaerobic environment), pelvic (post intrauterine device placement), abdominal (status post ruptured appendix or bowel perforation), and pulmonary (smokers with poor dental hygiene, aspiration of infective material) (Infect Drug Resist 2014;7:183)
  • Predisposing factors include poor oral hygiene, trauma, male gender, diabetes mellitus, immunosuppression, alcoholism and malnutrition (Infect Drug Resist 2014;7:183)
  • The filamentous bacteria are a normal commensal inhabitant of the oral and buccal cavities, gastrointestinal tract and female genitalia
  • The etiology of infection in skin is commonly linked with a traumatic injury, human bite or a perforating injury, which creates an anaerobic environment for Actinomyces israelii to grow in (J Clin Diagn Res 2014;8:YD03)
  • Caused by Actinomyces israelii in humans and Actinomyces bovis in animals
Clinical features
  • Localized pain, swelling and draining fistulas
  • Culture on chocolate agar media at 37 C
  • Gram stain is more sensitive than culture, especially if patient is on antibiotics
  • GMS stain highlights the filamentous bacteria, which are not visualized by H&E stain (Infect Drug Resist 2014;7:183)
  • Polymerase chain reaction (PCR) and nucleic acid probes are being developed for faster and more accurate identification
Case reports
  • High dose penicillin is necessary to penetrate areas of fibrosis and suppuration / granules
  • Drainage of abscesses or radical excision of sinus tracts
Clinical images

Contributed by Dr. Dhiraj B Nikumbh
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Multiple sinuses in foot

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Indurated lesion

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Lesion over back

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Left thigh lesion

Gross description
  • Firm, swollen region on the skin with multiple draining abscesses and fistula tracts
  • Pus draining yellow sulphur granules
Gross images

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Outer and inner surface and cross section of excised tissue

Microscopic (histologic) description
  • Lymphocytes, neutrophils, giant cells and fibroblasts
  • Bacterial colonies (sulphur granules) found at the center of the inflammatory reaction, composed of basophilic radiating filaments
Microscopic (histologic) images

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Colonies of Actinomyces species

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Actinomycin (sulfur) granules

Cytology description
  • Mixed inflammatory infiltrate, foreign body multinucleated giant cells and clumps of filamentous organisms
Cytology images

Contributed by Dr. Dhiraj B Nikumbh
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Mixed inflammatory infiltrate with clumps of fibrillar organisms and occasional foreign body giant cells

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Gram stain

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"Molar tooth" appearance

Positive stains
  • Gram positive
  • GMS stain demonstrates filamentous bacteria, which do not stain with H&E or PAS
Negative stains
Differential diagnosis
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