01In brief
Actinomyces israelii is a bacterial species associated with actinomycosis in humans. It is listed among the most common pathogenic Actinomyces species in people—under the spelling A. israeli in one reference—and a 1961 classification called it the chief etiological agent of human actinomycosis. The infection is exceedingly rare and can produce multiple abscesses and draining sinus tracts; its most prevalent form affects the jaws, neck, and face. The species has appeared under several names in earlier classifications, and historical accounts record some overlap between organisms attributed to it and to A. bovis.
02Overview
Actinomycosis is a chronic bacterial infection caused by anaerobic or microaerophilic Actinomyces species. These bacteria occur in the normal flora of humans and other animals, including the oral cavity, gastrointestinal tract, and human female genital tract. They may invade devitalized tissue when the integrity of a mucous membrane is compromised.[1]
The infection can produce multiple abscesses and draining sinus tracts, sometimes containing sulfur granules. Human actinomycosis is described as exceedingly rare and as typically affecting people between 20 and 50 years of age.[1]
03Origins and Classification
A 1961 reference work records the name Actinomyces israelii (Kruse) Lachner-Sandoval, 1898, and cites an 1891 work by Wolff and Israel. Earlier classifications used names including Streptothrix israeli, Nocardia israeli, and Corynebacterium israeli, reflecting changes and disagreements in how the organism was classified.[2]
That account characterized A. israelii as anaerobic and polymorphic, with branching filaments that could fragment, and reported no definite spores. It also described the organism as nonproteolytic and recorded acid production without gas from several sugars. These are historical descriptions rather than a current taxonomic or clinical review.[2]
Historical accounts associated the species with human oral habitats. The 1961 classification listed dental caries, tonsils, and natural cavities of humans and animals as habitats. A separate account reported repeated recovery from the human mouth and throat and treated the organism as indigenous to humans. It described human actinomycosis as endogenous in origin while noting that aspects of its pathogenesis remained uncertain.[2][3]
04Practice and Treatment
Thoracic actinomycosis primarily affects the lungs and surrounding structures. It may follow inhalation of the organism into the air passages and is usually associated with weight loss, night sweats, coughing, and high fever. Abdominal or pelvic infection may follow surgery for appendicitis or perforation of the stomach or large intestine. In rare cases, spread through the bloodstream can produce lesions in many parts of the body.[1]
Actinomycosis is treated with antibiotics. Surgical drainage or excision of accessible lesions may serve as an adjunct to antibiotic treatment.[1]
05Significance in Human Disease
The species is identified as one of the most common pathogenic Actinomyces species in humans, alongside A. gerencseriae. The reference making this identification spells the species name A. israeli, with one final “i.”[1]
Cervicofacial actinomycosis is the most prevalent form, accounting for at least half of human cases and primarily affecting the jaws, neck, and face. Lesions may appear after a wound in the mouth or a tooth extraction. The term “lumpy jaw” is also used for cervicofacial actinomycosis in cattle.[1]
The historical association between the organism, the healthy mouth, and human disease contributed to the view that infection could arise endogenously after disruption of oral tissues. The available historical account nevertheless cautioned that parts of the disease process, including the possible role of additional bacterial species, remained uncertain.[2][3]
06Controversies
Historical classifications separated A. israelii, described as causing most typical human infections, from A. bovis, associated with most cases of lumpy jaw in cattle. The boundary was not absolute: one A. israelii strain had reportedly been recovered from cattle, while a small number of human infections had been attributed to A. bovis.[2]
The same 1961 work summarized a comparison of 200 Actinomyces strains from oral cavities without actinomycosis and 11 strains from actinomycotic lesions. It reported two main types: one corresponding to A. naeslundii and another essentially identical to lesion isolates designated A. israelii.[2]
These reports illustrate historical uncertainty in classification. They do not establish the current taxonomic status of the distinctions.[2]
Sources
- 1Encyclopaedia Britannica, accessed on October 25, 2026.
- 2Internet Archive, Full text of "The actinomycetes", accessed on October 25, 2026.
- 3Internet Archive, Full text of "Microorganisms Indigenous To Man", accessed on October 25, 2026.
IsraelPedia Question & Answers
What is Actinomyces israelii?
Actinomyces israelii is a bacterial species associated with actinomycosis in humans. It is listed among the most common pathogenic Actinomyces species in people, and a 1961 classification called it the chief etiological agent of human actinomycosis. The infection is exceedingly rare and can produce abscesses and draining sinus tracts.
What parts of the body does actinomycosis caused by Actinomyces israelii most commonly affect?
Cervicofacial actinomycosis is the most prevalent form of human actinomycosis, accounting for at least half of cases and primarily affecting the jaws, neck, and face. Lesions may appear after a wound in the mouth or a tooth extraction.
How is actinomycosis treated?
Actinomycosis is treated with antibiotics. Surgical drainage or excision of accessible lesions may be used as an adjunct to antibiotic treatment.
How was Actinomyces israelii classified under earlier names?
Earlier classifications used names including Streptothrix israeli, Nocardia israeli, and Corynebacterium israeli. These names reflected changes and disagreements in how the organism was classified; the historical accounts do not establish its current taxonomic status.
What did historical accounts say about Actinomyces israelii in the human mouth?
Historical accounts associated Actinomyces israelii with human oral habitats, including dental caries, tonsils, and natural cavities. One account reported repeated recovery from the human mouth and throat and treated the organism as indigenous to humans. It described human actinomycosis as endogenous in origin, while noting that aspects of its pathogenesis remained uncertain.
How did historical classifications distinguish Actinomyces israelii from Actinomyces bovis?
Historical classifications associated Actinomyces israelii with most typical human infections and Actinomyces bovis with most cases of lumpy jaw in cattle. The distinction was not absolute: one A. israelii strain had reportedly been recovered from cattle, and a small number of human infections had been attributed to A. bovis. These reports do not establish the current taxonomic status of the distinctions.