ACTINOMYCETES

Actinomycetes

Actinomycetes is a group of Gram-positive bacteria known for their filamentous, branching growth pattern, similar to fungi. They are widely distributed in soil and are known for their ability to produce a variety of antibiotics. The genus Actinomyces is the most clinically significant, with Actinomyces israelii being a common pathogen in humans. Actinomycosis, a chronic granulomatous infection, is the most well-known disease caused by these bacteria.

Microscopic Appearance

• Shape:

  • Filamentous and branching, resembling the mycelium of fungi.

  • Can fragment into rod-shaped or coccoid elements.

• Gram Stain:

  • Gram-positive, although they may appear Gram-variable in older cultures.

• Non-Motile:

  • They do not have flagella and are therefore non-motile.

• Special Stains:

  • May require special staining techniques, such as modified acid-fast staining, for better visualization in certain species.

• Give soil the “earthy” smell

• Straight, curved or pleomorphic

• Unicellular like bacteria but produce mycelium which is non septate and more slender

• Note : Morphology resembles to fungi, cellular organization typical of bacteria

Virulence Factors

• Filamentous Growth:

  • Enables the bacteria to invade tissues and form extensive networks, contributing to the chronic nature of the infection.

• Sulfur Granules:

  • In tissue infections, Actinomyces often produce characteristic yellowish sulfur granules, which are aggregates of the bacteria surrounded by inflammatory cells.

• Adherence:

  • Ability to adhere to mucosal surfaces, particularly in the oral cavity, leading to colonization and subsequent infection.

• Immune Evasion:

  • Can persist in host tissues by evading the immune response, often leading to chronic infections.

Pathogenesis

• Entry and Colonization:

  • Actinomyces species are part of the normal flora of the oral cavity, gastrointestinal tract, and female genital tract. They can cause infection when mucosal barriers are disrupted, such as after dental procedures, trauma, or surgery.

• Tissue Invasion:

  • The bacteria invade tissues, leading to the formation of abscesses and sinus tracts. These tracts can discharge pus containing sulfur granules.

• Chronic Inflammation:

  • The infection typically progresses slowly, leading to chronic granulomatous inflammation, fibrosis, and the formation of draining sinuses.

Clinical Manifestations

• Cervicofacial Actinomycosis:

  • The most common form of actinomycosis, often associated with poor oral hygiene or dental procedures.

  • Presents as a slowly progressing mass in the jaw or neck region, with the formation of abscesses and sinus tracts that discharge pus containing sulfur granules.

• Thoracic Actinomycosis:

  • Involves the lungs and chest wall, often presenting with chronic cough, chest pain, and weight loss. Can lead to pleural effusion and empyema.

• Abdominal Actinomycosis:

  • Involves the gastrointestinal tract, often presenting with a mass, pain, and symptoms mimicking other conditions such as appendicitis or diverticulitis.

• Pelvic Actinomycosis:

  • Can occur in women with intrauterine devices (IUDs) and may present with pelvic pain, fever, and vaginal discharge.

• Central Nervous System (CNS) Actinomycosis:

  • Rare, but can cause brain abscesses, meningitis, or other CNS infections.

Lab Diagnosis

• Microscopy:

  • Direct examination of pus or tissue specimens may reveal Gram-positive, branching filaments and sulfur granules.

• Culture:

  • Actinomyces species are slow-growing and may require up to two weeks to grow on culture media. They grow best in anaerobic or microaerophilic conditions on enriched media such as blood agar.

  • Anaerobic bacteria and grows well in presence of 5 10% co2.

  • Optimum temperature 35 37 degree Celsius

  • Grow on brain heart infusion agar/broth andthioglycolate agar containing o.12% 0.2% rabbit blood.

• Histopathology:

  • Tissue biopsy with histopathological examination can show characteristic sulfur granules surrounded by a chronic inflammatory response.

• Molecular Techniques:

  • PCR and sequencing can be used for species identification in complex cases.

Treatment

• Antibiotics:

  • Prolonged antibiotic therapy is usually required, often starting with high-dose intravenous penicillin G for 4-6 weeks, followed by oral penicillin or amoxicillin for several months.

  • Alternatives for penicillin-allergic patients include doxycycline, clindamycin, or erythromycin.

• Surgical Intervention:

  • May be necessary to drain abscesses or debride infected tissue, particularly in cases with extensive fibrosis or sinus tract formation.

• Prevention:

  • Good oral hygiene and prompt treatment of dental infections can reduce the risk of cervicofacial actinomycosis.

  • Careful management of IUDs and monitoring for symptoms in women using these devices can help prevent pelvic actinomycosis.