Actinomyces israelii

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Actinomyces israelii
Scanning electron micrograph of Actinomyces israelii.
Scanning electron micrograph of Actinomyces israelii.
Scientific classification
Domain: Bacteria
Phylum: Actinobacteria
Order: Actinomycetales
Family: Actinomycetaceae
Genus: Actinomyces
Species: A. israelii
Binomial name
Actinomyces israelii
(Kruse 1896)
Lachner-Sandoval 1898

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This page is about microbiologic aspects of the organism(s).  For clinical aspects of the disease, see Actinomycosis.

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]


Actinomyces israelii is a species of Gram-positive, rod-shaped bacteria within the Actinomyces. Known to live commensally on and within humans, A. israelii is an opportunistic pathogen and a cause of actinomycosis. Many physiologically diverse strains of the species are known to exist, though all are strict anaerobes.[1]


Actinomycosis is most frequently caused by A. israelii. It is a normal colonizer of the vagina,[2] 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 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.


  1. Levinson, W. Review of Medical Microbiology and Immunology. 2010:McGraw Hill.
  2. Hoffman, Barbara (2012). Williams gynecology, 2nd edition. New York: McGraw-Hill Medical. p. 65. ISBN 0071716726.