Actinomyces israelii

Pathogenesis

Actinomycosis is most frequently caused by A. israelii. It is a normal colonizer of the vagina, colon, and mouth. Infection is established first by a breach of the mucosal barrier during various procedures (dental, gastrointestinal), aspiration, or pathologies such as diverticulitis. The chronic phase of this disease is also known as the "classic phase" because the acute, early phase is often missed by health care providers. This is characterized by slow, contiguous growth that ignores tissue planes and forms a sinus tract that can spontaneously heal and recur, leading to a densely fibrotic lesion. This lesion is often characterized as "wooden". Sulfur granules form in a central purulence surrounded by neutrophils. This conglomeration of organisms is virtually diagnostic of A. israelii.