Gram-positive rod-shaped bacteria within the Actinomyces.
Known to live commensally on and within humans (A. israelii is a normal colonizer of the vagina, colon, and mouth).
Opportunistic pathogen and a cause of actinomycosis. Infection is established first by a breach of the mucosal barrier during various procedures (dental, GI), aspiration, or pathologies such as diverticulitis.
Many physiologically diverse strains of the species are known to exist, though all are strict anaerobes.
Manifestations of disease: Oral-cervicofacial disease is the most common form of actinomycosis. Another form of actinomycosis is thoracic disease, which is often misdiagnosed as a neoplasm, as it forms a mass that extends to the chest wall. Abdominal disease is another manifestation of actinomycosis.
Actinomycosis may be considered when a patient has chronic progression of disease across tissue planes that is mass-like at times, sinus tract development that may heal and recur, and refractory infection after a typical course of antibiotics.
Important considerations: The choice of an agent should be based on local antimicrobial sensitivities, site of infection, cost, and comorbid conditions. Generally, the most common agents/regimens are listed first. Listed dosages may need to be adjusted for renal dysfunction.