Actinomyces israelii

Actinomyces israelii:

Actinomyces israelii
Scanning electron micrograph of Actinomyces israelii.
Scientific classification
Domain: Bacteria
Phylum: Actinobacteria
Order: Actinomycetales
Family: Actinomycetaceae
Genus: Actinomyces
Species: A. israelii


Is an uncommon cause of appendicitis. Rarely, A. israelii can lead to infections of the small intestine, appendix, or colon. Histologically, the long filamentous organisms stain dark blue on routine H&E preparations and are particularly easy to recognize when associated with characteristic sulfur granules. Active inflammation in the mucosal wall is typically present, and fistula formation, rupture of the appendix, and abscess formation may complicate the clinical course. Actinomyces turicensis has also been implicated in appendicitis and is frequently accompanied by aerobic bacterial isolates of the Streptococcus anginosus group.


Human actinomycosis, a chronic, granulomatous infectious disease, has been recognized for a long time and its causative agent, originally named Streptothrix israeli (currently Actinomyces israelii), was described in 1896 by Kruse . It was not until 1951 that another Actinomyces species, Actinomyces naeslundii, was implicated in actinomycotic lesions in humans while Actinomyces odontolyticus and Actinomyces viscosus (first named as Odontomyces viscosus) were described in 1958 and 1969, respectively

It is well established that actinomycosis is an endogenous infection. The causative Actinomyces species reside on mucosal surfaces and gain access to deeper tissues via trauma, surgical procedures, or foreign bodies, which disrupt the mucosal barrier. Inside the tissue, these bacteria form masses consisting of aggregates of branching, filamentous bacilli (Actinomycosis is defined as a hard mass-type lesion with a specific histopathological structure. There are a large number of case reports of actinomycosis in the literature, but in most cases, diagnosis has been based solely on clinical and histopathological findings. In the majority of early reports, microbiological confirmation of diagnosis was lacking. Even when microbiological assessment was included, culture was typically the only method used. If, however, antimicrobial treatment had been started before sample collection, the results of culture may be falsely negative. The increasing introduction of molecular bacterial detection and identification methods is helping to overcome such problems.

A large number of Actinomyces species have been described since the description of A. israelii, A. naeslundii, A. odontolyticus, and A. viscosus. In addition, reassignments within some species, such as A. naeslundii and A. viscosus, have occurred However, only some human-associated Actinomyces species, including A. israelii, Actinomyces gerencseriae, and Actinomyces graevenitzii, may be involved in classical actinomycosis .A wide range of Actinomyces species are being increasingly associated with infections at many body sites. Actinomyces meyeri, Actinomyces neuii, and Actinomyces turicensis are emerging as important causes of such infections.

Although actinomycosis is relatively rare, at least in Western populations , recently reported observations implicating A. meyeri in brain abscesses and Actinobaculum schaalii (currently Actinotignum schaalii) in urosepsis and the introduction of advanced microbiological techniques, which can identify even very fastidious organisms, have resulted in an increased awareness of Actinomyces and other Gram-positive, non-spore-forming bacilli in clinical microbiology.

To date, 25 validly published Actinomyces species from human material have been described . Of these, the descriptions of 13 species occurred solely during this century. In the present review, we aim to give a comprehensive overview of human Actinomyces and closely related organisms and their roles in different types of actinomycoses and other infections.


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 not all are strict anaerobes. It was named after the German Surgeon, James Adolf Israel (1848–1926), who studied the organism for the first time in 1878. Is an anaerobic gram-positive bacterium that causes purulent abscesses and sinus tract formation? This organism can affect the cervicofacial, pulmonary/thoracic, gastrointestinal, and female reproductive tract. This section focuses on cervicofacial actinomycosis, which represents the majority of infections caused by this organism.

Clinical Features and Presentation:

In cervicofacial actinomycosis, patients present with a hard swelling associated with the jaw. As the swelling progresses, a bluish discoloration of the skin appears. Over time, a fistulous abscess forms within the hard swelling and sinus tracts develop. A yellowish purulent material is usually discharged from these sinuses.



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.


Actinomyces israelli is curable and can be treated with antibiotics. It has been shown that both a sodium hypochlorite solution and calcium hydroxide to be highly effective in killing A. israelii when it has caused infection in the mouth.


Actinomyces israelii has long been recognized as a causative agent of actinomycosis. During the past 3 decades, a large number of novel Actinomyces species have been described. Their detection and identification in clinical microbiology laboratories and recognition as pathogens in clinical settings can be challenging. With the introduction of advanced molecular methods, knowledge about their clinical relevance is gradually increasing, and the spectrum of diseases associated with Actinomyces and Actinomyces-like organisms is widening accordingly; for example, Actinomyces meyeri, Actinomyces neuii, and Actinomyces turicensis as well as Actinotignum (formerly Actinobaculum) schaalii are emerging as important causes of specific infections at various body sites. In the present review, we have gathered this information to provide a comprehensive and microbiologically consistent overview of the significance of Actinomyces and some closely related taxa in human infections.

You may also like...

Leave a Reply

Your email address will not be published. Required fields are marked *

Translate »