Actinomyces israelii is a bacterium, not a fungus, despite its name. This organism is a common inhabitant of the human body, usually residing without causing harm. It is found in various parts of the body as part of the normal microscopic community. Under specific conditions, however, this bacterium can cause an infection.
Natural Habitat and Transmission
Actinomyces israelii is found in the human body’s normal microbial populations. It is common in the oral cavity, particularly in dental plaque, tonsillar crypts, and on teeth surfaces. This bacterium also inhabits the gastrointestinal tract, including the colon, and is present in the female genital tract.
Infection with Actinomyces israelii is not contagious. Infections are endogenous, originating from the individual’s own bacteria. They develop when there is a break or disruption in the mucosal barrier. Breaches can occur from dental procedures like extractions, surgical operations, physical trauma, or the presence of foreign bodies, such as an intrauterine device (IUD).
The Infection Process and Symptoms
The infection caused by Actinomyces israelii is known as actinomycosis. This condition is slow-growing and progressive, often developing over weeks or months. The infection leads to the formation of hard, non-tender masses or abscesses within affected tissues. These lesions can expand and develop draining sinus tracts that discharge pus to the skin surface or into other body cavities.
A distinctive sign of actinomycosis is “sulfur granules” within the pus or infected tissue. These yellowish, macroscopic specks are dense microcolonies of Actinomyces bacteria embedded in a protein-polysaccharide matrix. Actinomycosis can affect various parts of the body, leading to different clinical forms.
The cervicofacial form, the most common, presents as a lump or swelling in the jaw, neck, or face, often following a dental procedure or oral trauma. Thoracic actinomycosis affects the lungs and chest wall, causing cough, chest pain, and fever, sometimes mimicking other lung diseases.
Abdominal actinomycosis can involve any part of the gastrointestinal tract or surrounding organs, leading to symptoms like abdominal pain, fever, and weight loss. Pelvic actinomycosis, primarily seen in women, is often associated with the use of IUDs and can cause lower abdominal pain, vaginal discharge, and pelvic masses.
Diagnosis and Medical Evaluation
Diagnosing actinomycosis is challenging because the bacteria are difficult to grow in standard laboratory cultures. Actinomyces israelii is an anaerobic bacterium, making its isolation from clinical samples complex. A physician’s clinical suspicion, based on the patient’s medical history and the lesion’s characteristic appearance, is highly important. The slow progression of symptoms and the presence of indurated masses or draining sinuses can raise suspicion.
Diagnostic methods involve obtaining tissue samples through biopsy or by aspirating pus from an abscess. These samples are examined microscopically for characteristic sulfur granules and branching filamentous bacterial forms. While culturing the organism can confirm the diagnosis, it often requires specialized anaerobic culture techniques and prolonged incubation periods, sometimes up to 2-3 weeks. Imaging studies, such as computed tomography (CT) scans, are frequently used to determine the extent of the infection and to identify affected organs or bone involvement.
Treatment Approaches
Treatment for actinomycosis involves a prolonged course of high-dose antibiotics. Penicillin is the antibiotic of choice given its effectiveness against Actinomyces israelii. The initial phase of treatment often involves intravenous administration of penicillin for two to six weeks, followed by a switch to oral antibiotics for several months.
The extended duration of antibiotic therapy, which can range from six to twelve months or even longer, is necessary to ensure complete eradication of the bacteria. This prolonged treatment is due to the dense, fibrotic nature of the infected tissues, which can be poorly vascularized, making it difficult for antibiotics to penetrate effectively and reach all bacteria. In addition to antibiotics, surgical intervention may be required. This includes draining large abscesses and performing debridement of damaged tissue. Surgical removal of infected foreign bodies, such as an IUD, is also often necessary to resolve pelvic infections.
References
Actinomyces israelii. ScienceDirect. [https://www.sciencedirect.com/topics/medicine-and-dentistry/actinomyces-israelii](https://www.sciencedirect.com/topics/medicine-and-dentistry/actinomyces-israelii)
Actinomycosis. StatPearls. [https://www.ncbi.nlm.nih.gov/books/NBK557782/](https://www.ncbi.nlm.nih.gov/books/NBK557782/)