Last reviewed 01/2018

Actinomycosis is rare, chronic bacterial infection which results in a slowly progressive granulomatous disease.  

  • the bacteria which is a filamentous Gram positive anaerobic bacteria from the Actinomycetaceae family (genus Actinomyces) is a normal colonizing organism of the human oropharynx, gastrointestinal tract, and urogenital tract. 
  • it is mainly an endogenous infection where a breech in the mucous membrane results in bacteria invading the local structures and organs and causing a disease
  • A  israelii is the commonest  human pathogen while less common species include A naeslundii, A odontolyticus, A viscosus, A meyeri, A turicensis, and A radingae.

Often the bacteria coexists with other normal commensals  e. g - Aggregatibacter actinomycetemcomitans (previously Actinobacillus actinomycetemcomitans), fusobacteria, bacteroides, staphylococci (including S aureus),streptococci (including β haemolytic streptococci and S pneumoniae), or Enterobacteriaceae but  precise pattern of organisms depends on the site of infection (1). 

The infection spreads along the fascial planes and occasionally by the blood-stream, but not via the lymphatics.

Thermophilic actinomycetes found in hay are the cause of the extrinsic allergic alveolitis termed farmer's lung.