Actinomyces spp. are a group of bacteria commonly found within the human body. Though often harmless, these microorganisms can sometimes lead to a chronic infection known as actinomycosis. Understanding how these bacteria cause disease is important for recognizing and managing potential health issues. This article explores the nature of Actinomyces and their transition from typical inhabitants to agents of infection.
Defining Actinomyces and Their Common Habitats
Actinomyces are Gram-positive bacteria, meaning they retain a purple stain. They are anaerobic or microaerophilic, thriving in environments with little to no oxygen. Individual bacteria are rod-shaped, but their colonies often form branched, filamentous networks, leading to their historical misclassification as fungi, reflected in their name, meaning “ray fungus.”
These bacteria are part of the normal human microbiome. They are commonly found in the oral cavity, residing in dental plaque, tonsillar crypts, and on teeth surfaces. Actinomyces species also inhabit the gastrointestinal tract and the female genitourinary tract. They are usually found on mucosal surfaces, but not typically on the skin.
From Commensal to Pathogen
Actinomyces species are opportunistic pathogens, causing infection when specific conditions disrupt the body’s natural defenses. This transition occurs when mucosal barriers are breached, often by trauma, surgical procedures, or foreign bodies, allowing bacteria to access deeper tissues.
Once in deeper tissues, the bacteria aggregate into masses of branching, filamentous bacilli. They thrive in low-oxygen environments, which tissue damage or foreign bodies can create, promoting their growth. Actinomyces infections are often polymicrobial; other bacteria, particularly those from the Streptococcus genus, frequently accompany them, enhancing Actinomyces growth by inhibiting host defenses and reducing oxygen tension.
Common Forms of Actinomycosis
Actinomycosis can manifest in several forms, often characterized by abscesses and draining sinus tracts.
Cervicofacial Actinomycosis
The most common presentation is cervicofacial actinomycosis, known as “lumpy jaw,” accounting for 50–70% of cases. This form typically follows dental procedures, oral or facial trauma, or poor oral hygiene. It presents as a slowly growing, firm, often painless swelling in the jaw or neck. Abscesses may develop, forming draining sinuses that discharge pus, which can contain yellowish “sulfur granules.”
Thoracic Actinomycosis
Making up 15–20% of cases, thoracic actinomycosis usually results from aspirating oral secretions into the lungs. Symptoms include a persistent cough, sputum production, chest pain, and difficulty breathing, often mimicking other lung conditions like tuberculosis or tumors. The infection can spread to the pleura, pericardium, and chest wall, potentially leading to sinus tracts that extend to the skin.
Abdominal Actinomycosis
This accounts for 10–20% of cases and typically arises from a break in the gastrointestinal mucosa, such as after surgery, appendicitis, or diverticulitis. Symptoms are often non-specific and slowly progressive, including fever, weight loss, abdominal pain, and changes in bowel habits. Abdominal masses can form, and draining sinuses may extend to the abdominal wall or perianal area.
Pelvic Actinomycosis
Though less common, pelvic actinomycosis is often linked to long-term IUD use. The IUD can cause irritation and trauma to the uterine lining, facilitating bacterial invasion. Women may experience lower abdominal discomfort, abnormal vaginal bleeding, or unusual vaginal discharge. Other less frequent forms include central nervous system involvement and disseminated infections, where the bacteria spread through the bloodstream to various organs.
Identifying and Treating Actinomycosis
Diagnosing actinomycosis can be challenging due to its slow progression and non-specific symptoms, which can resemble other infections or malignancies. Clinical suspicion, based on chronic lesions, abscesses, or draining sinuses, is an initial step. Imaging techniques like X-rays and CT scans help visualize the infection’s extent.
Laboratory confirmation involves culturing bacteria from pus or tissue biopsy specimens. This requires prolonged incubation due to their slow growth and anaerobic nature. The presence of “sulfur granules”—small, yellowish aggregates of bacterial filaments—in pus or tissue strongly indicates actinomycosis. Microscopic examination of Gram-stained samples is often more sensitive than culture, especially if antibiotics have already been administered.
Treatment typically involves long-term, high-dose antibiotic therapy, as lesions are often dense with limited blood supply. Penicillin G is the preferred antibiotic, administered intravenously for several weeks, followed by oral penicillin V or amoxicillin for an extended period, ranging from 6 to 12 months. For patients with penicillin allergies, alternatives like tetracycline, doxycycline, minocycline, clindamycin, or erythromycin can be used. Surgical drainage of abscesses and removal of infected tissue may also be necessary, particularly for large abscesses or extensive spread.