Gram-Positive Anaerobes: Propionibacterium, Peptococcus niger, Actinomyces and actinomycosis

Question 1

Propionibacterium

Answer 1

Propionibacterium is an anaerobic, gram-positive rod commonly found on skin. The most important species is Propionibacterium acnes (now Cutibacterium acnes), which contributes to acne vulgaris by breaking down sebum and inducing inflammation. It can also cause prosthetic device infections and postoperative shoulder infections. It’s slow-growing and part of normal flora, making it a contaminant in blood cultures. Treatment includes benzoyl peroxide, topical clindamycin, and systemic antibiotics for deep infections.

Question 2

Peptococcus niger

Answer 2

Peptococcus niger is an anaerobic, gram-positive coccus found in the mouth, respiratory tract, and intestines. It is part of the normal flora and causes infections like brain abscesses, dental infections, and aspiration pneumonia, usually as part of polymicrobial anaerobic infections. It is sensitive to penicillin, metronidazole, and clindamycin. Rarely isolated alone.

Question 3

Actinomyces

Answer 3

Actinomyces species are filamentous, branching, anaerobic, gram-positive rods that resemble fungi. Found in the oral cavity, GI tract, and female genital tract. The most common pathogen is Actinomyces israelii. They cause actinomycosis—a chronic granulomatous infection with abscesses, draining sinuses, and sulfur granules (yellow aggregates of organisms seen microscopically). Common sites: cervicofacial (jaw—’lumpy jaw’), thoracic, and abdominal regions. Actinomyces infections follow dental trauma or surgery. Diagnosis: gram stain and culture of sulfur granules. Treatment: high-dose penicillin G for weeks to months; surgery may be needed for drainage.