Infectious colitis


Last author update: 1 January 2017
Last staff update: 5 May 2021

Copyright: 2003-2023,, Inc.

PubMed Search: actinomycosis

Elliot Weisenberg, M.D.
Page views in 2022: 4,692
Page views in 2023 to date: 10,944
Cite this page: Weisenberg E. Actinomycosis. website. Accessed September 27th, 2023.
Definition / general
  • Infection of large intestine by actinomycotic microorganisms
  • Colonic actinomycosis is a subset of abdominal actinomycosis, but some sources do not discriminate between actinomycosis of abdomen and pelvis
  • Other common sites are oral cervicofacial actinomycosis ("lumpy jaw", see secondary chronic osteomyelitis), skin, thoracic and pelvic (cervix, kidney, ovary)
  • Rare, but abdominal actinomycosis comprises 15 - 20% of actinomycosis in humans
  • Males are more commonly affected
  • Most common site is cecum, most often with concurrent ileal disease
  • Some cases are secondary to disease in appendix or female genital tract
  • Due to infection by anaerobic or microaerophilic, saprophytic bacteria of genus Actinomyces, a normal commensal of mouth, large intestine, vagina
  • Disruption of mucosa is necessary for disease - causes are trauma, surgery, diverticular disease, ingestion of foreign body, or less commonly other inflammatory processes
    • In surgery related cases, disease may appear months after perforation leading to appendectomy or bowel resection, but without evidence of actinomycosis at the time
  • In some cases, no inciting event is identified; rare cases may originate through hematogenous spread
  • While actinomycotic colonies may dominate the histologic picture, it is likely that companion, or "co-pathogenic" bacteria may also be necessary for disease to occur, possibly by lowering oxygen tension
  • Actinomyces israelii is the most common etiologic agent; however, at least five other species are implicated in human disease
  • Using comparative 16s ribosomal RNA, some bacteria traditionally associated with actinomycotic disease have been reclassified as Aracanobacterium, Actinobaculum or Cellulomonas
Clinical features
  • Usually indolent disease, but more severe in immunocompromised patients
  • Patients usually present with non-specific symptoms including abdominal pain, fever, change in bowel habits, sensation of a mass
  • Imaging studies reveal a mass-like lesion, cystic lesion or an abscess, often suggestive of malignancy
  • May coexist with other inflammatory lesions of colon with fistula or sinuses
  • Clumps of yellow bacteria known as sulfur granules are characteristically present
  • No cases of human to human transmission have been reported and Actinomyces has not been cultured from nature
  • Usually by tissue biopsy or resection where the characteristic microorganisms are seen
  • Abdominal actinomycosis is rarely suspected clinically and most patients are diagnosed after major surgery
  • Diagnosis by microbiologic culture is uncommon as strict anaerobic conditions are necessary and antibiotics interfere with growth in culture
Prognostic factors
  • Most patients respond well to therapy
Case reports
  • Prolonged high dose antibiotics
  • Even with advanced clinical disease, most patients can be effectively treated with medical management alone; however, this is very uncommon with abdominal disease
Gross images

Images hosted on other servers:
Missing Image

Sigmoid colon mass

Microscopic (histologic) description
  • Characteristic clumps of basophilic filamentous bacteria in a vaguely rosette-like configuration surrounded by acute inflammatory cells are characteristic
  • Acute inflammation is accompanied by dense fibrosis described as "woody"
  • Eosinophilic clubs may be found at periphery (Splendore-Hoeppli phenomena)
  • Granulomatous inflammation may be present
Microscopic (histologic) images

Contributed by Asmaa Gaber Abdou, M.D.
Missing Image Missing Image Missing Image

Intestinal actinomycosis

Images hosted on other servers:
Missing Image Missing Image

Bacteria and sulfur granules

Missing Image Missing Image

Colonies of actinomyces

Missing Image

Gram+ staining

Missing Image

Filamentous microorganisms (GMS)

Positive stains
  • Gram positive, GMS, basophilic with H&E
Negative stains
Differential diagnosis
Back to top
Image 01 Image 02