Actinomyces spp

From Dog
Actinomyces endophthalmitis in the right eye of a young rottweiler with diffuse corneal edema, mucopurulent ocular discharge, conjunctival hyperemia, and chemosis[1]

Actinomyces spp are Gram-positive facultatively anaerobic or strictly anaerobic spore-forming bacteria normally found in the oropharynx of dogs[2].

Once thought to be a fungus, they form fungus-like branched networks of hyphae.

Species which are pathogenic to dogs include:

  • Actinomyces weissii - gingivitis[3]
  • Actinomyces turicensis[4]
  • Actinomyces coleocanis[5]
  • Actinomyces hordeovulneris[6]

Actinomycosis is usually diagnosed in middle-aged, large breed, outdoor dogs; when the skin and subcutaneous tissues are involved, it is often characterized by draining fistulous tracts, if the chest cavity is involved, pyothorax[7][8].

The pathogenesis in dogs usually involves inhalation or ingestion of grass awns or penetration of skin and soft tissue by a foreign body such as grass awns[9]. Once an Actinomyces spp infects these tissues, granulomas and draining fistulous tracts develop[10].

The cervicofacial region, pulmonary parenchyma, pleura, pericardium, urinary bladder[11], retroperitoneal space, limbs, and subcutaneous tissues are the most commonly affected areas[12].

These bacteria are commonly isolated from the oral mucosa[13] but can be found systemically with septic wounds[14], pneumonia and ocular disease[15].

Successful treatment of systemic actinomycosis involves prolonged (4–6 wk) administration of systemic antibiotics. Beta-lactam antibiotics, such as penicillin or ampicillin, are the antibiotics of choice for Actinomyces spp infections, although cephalexins and aminoglycosides have proven effective[16].


  1. Barnes LD & Grahn BH (2007) Actinomyces endophthalmitis and pneumonia in a dog. Can Vet J 48(11):1155-1158
  2. Hardie EM (1990) Actinomycosis and nocardiosis. In: Greene CE, editor. Infectious Diseases of the Dog and Cat. Philadelphia: WB Saunders. pp:585–590
  3. Hijazin M et al (2012) Further characteristics of Actinomyces weissii, a novel species isolated from the oral cavity of dogs. Berl Munch Tierarztl Wochenschr 125(7-8):332-336
  4. Junius G et al (2004) Mitral valve endocarditis in a labrador retriever caused by an actinomyces species identified as Actinomyces turicensis. J Vet Intern Med 18(6):899-901
  5. Hoyles L et al (2002) Actinomyces coleocanis sp. nov., from the vagina of a dog. Int J Syst Evol Microbiol 52(4):1201-1203
  6. Pelle G et al (2000) Actinomycosis of dogs caused by Actinomyces hordeovulneris. J Comp Pathol 123(1):72-76
  7. Rooney MB & Monnet E (2002) Medical and surgical treatment of pyothorax in dogs: 26 cases (1991-2001). J Am Vet Med Assoc 221(1):86-92
  8. Mertens MM et al (2005) Pleural and extrapleural diseases. In: Ettinger SJ, Feldman EC, editors. Textbook of Veterinary Internal Medicine. 6. St Louis, Missouri: Elsevier Saunders. pp:1272–1283
  9. Brennan KE & Ihrke PJ (1983) Grass awn migration in dogs and cats: A retrospective study of 182 cases. J Am Vet Med Assoc 182:1201–1204
  10. Kirpensteijn J & Fingland RB (1992) Cutaneous actinomycosis and nocardiosis in dogs: 48 cases (1980–1990). J Am Vet Med Assoc 201:917–920
  11. Billington SJ et al (2002) Isolation of Arcanobacterium (Actinomyces) pyogenes from cases of feline otitis externa and canine cystitis. J Vet Diagn Invest 14(2):159-162
  12. Couto SS et al (2000) Pyogranulomatous meningoencephalitis due to Actinomyces sp. in a dog. Vet Pathol 37:650–652
  13. Hijazin M et al (2012) Actinomyces weissii sp. nov., isolated from dogs. Int J Syst Evol Microbiol 62(8):1755-1760
  14. Doyle JL et al (2009) Intra-thoracic pyogranulomatous disease in four working dogs. N Z Vet J 57(6):346-351
  15. Ledbetter EC & Scarlett JM (2008) Isolation of obligate anaerobic bacteria from ulcerative keratitis in domestic animals. Vet Ophthalmol 11(2):114-122
  16. Papich MG & Bidgood T (2005) Antimicrobial drug therapy. In: Ettinger SJ, Feldman EC, editors. Textbook of Veterinary Internal Medicine. 6. St Louis, Missouri: Elsevier Saunders. pp:498–503