Aetiology

Actinomycosis is caused by branching gram-positive bacteria. Actinomycosis was first described in 1878 and first isolated under anaerobic conditions in 1891.[9][10]

Actinomyces are strict or facultative anaerobes. The bacteria form diphtheroidal or coccoidal filaments and resemble fungi. They are part of the normal intestinal and oral flora and are particularly located in periodontal pockets, dental plaque, and dental caries. The main species involved in human disease is Actinomyces israelii. However, more than 30 species have been linked to human disease.[11]Actinomyces are almost invariably isolated as part of a polymicrobial flora. The significance of these co-isolated bacteria in the pathogenesis of actinomycosis remains unclear.[12]

Pathophysiology

Because actinomycosis is an infection with various manifestations, clinical features vary. Actinomycetes acquire pathogenicity through invasion of breached or necrotic tissue. Once infection is established, the host mounts an intense inflammatory response (i.e., with suppuration and granuloma formation). Fibrosis may then follow. Infection typically spreads contiguously and invades surrounding tissues or organs. Ultimately, the infection produces draining sinus tracts, which are a hallmark of the infection.[1][4][7][8]​[13][14][15][16][17]​​[18]​​​

Infections are seen most commonly in the cervicofacial area (50% to 70%), followed by the abdomen and pelvis (10% to 20%).​[13][19]​[20]​​ Other manifestations, such as thoracic, hepatic or CNS actinomycosis, are much rarer and are found only as sporadic case reports.[21][22][23][24][25][26]

Cervicofacial actinomycosis often starts after a tissue injury or orofaciomaxillary trauma. In its initial stages it is characterised by soft-tissue swelling of the perimandibular area. Spread occurs over time into adjacent tissues. As a consequence of infection, fistulae (sinus tracts) develop, and these discharge purulent material containing granules with a yellow sulfur-like appearance (termed sulfur granules). Invasion of the cranium or the bloodstream is seen very rarely, but may occur if the disease is misdiagnosed or left untreated.[13][17]

Actinomycosis frequently follows surgery. The disease tends to spread locally in a contiguous fashion, disregarding tissue borders. Lymphadenopathy is not typical, and haematogenous dissemination is rare. Because of the slow growth of the pathogen, disease may develop over months to years before diagnosis is made.[13][17]

Classification

Taxonomic classification

Actinomycetes are a group of gram-positive bacteria with high guanine-cytosine content. Most actinomycetes of medical or economic significance are in the subclass Actinobacteridae, order Actinomycetales.

Use of this content is subject to our disclaimer