Makindo Medical Notes Comprehensive Medical Encyclopedia | Education for Healthcare Professionals

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Prevotella (Bacteroides) melaninogenica

📖 About

Prevotella melaninogenica (formerly Bacteroides melaninogenica) → Gram-negative, anaerobic bacterium.
Part of the normal oral, GI, and genital flora but opportunistic in disease.
Produces melanin → black-pigmented colonies on culture media.

🔬 Characteristics

Gram-negative, strict anaerobe.
Melanin production → diagnostic black pigmentation in vitro.
Opportunistic pathogen → pathogenic if barriers disrupted.

🏠 Source

Normal flora of oral cavity, GI tract, and genital tract.
Becomes pathogenic in wounds (esp. human bites 👄), trauma, or aspiration events.

⚠️ Pathogenicity

Human bite wound infections: Common due to its oral flora reservoir.
Chest infections: Aspiration pneumonia, lung abscesses, empyema → esp. in poor dental hygiene or immunocompromised patients.
Periodontal disease: Contributes to gum disease and oral abscesses.
UTIs: Rare, usually linked to instrumentation or comorbidities.

🧬 Antibiotic Resistance

Beta-lactamase production → resistance to many penicillins ❌.
Macrolide (e.g. erythromycin) and clindamycin resistance reported in some strains.

💊 Management

Antibiotics:
- Metronidazole → highly effective against anaerobes.
- Amoxicillin–clavulanate → overcomes beta-lactamase resistance.
- Carbapenems → reserved for severe or resistant cases.
Surgery: Drainage or debridement if abscess or wound infection present.

⚠️ Exam pearl: Think Prevotella melaninogenica in human bite wound infections and aspiration pneumonia with black-pigmented anaerobes. Management = metronidazole ± surgical drainage.

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Makindo Medical Notes