Eikenella corrodens is a facultative anaerobic Gram-negative bacillus.
Best known for causing infections following human bites (“clenched-fist injuries”) and oral cavity infections.
It belongs to the HACEK group of organisms (Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, Kingella), which are notable causes of endocarditis.

🔬 Characteristics

Gram-negative slender rods (bacilli) 🦠.
Forms colonies that produce pitting/corrosion on agar (hence the name “corrodens”).
Capable of both aerobic and anaerobic growth, especially on enriched media such as blood agar or chocolate agar.
Often has a “bleach-like” odour in culture.

🌍 Source

Part of the normal flora of the human oral cavity and nasopharynx.
Also found in the gastrointestinal and genitourinary tracts.
Introduced into tissues by bites, fist injuries, or aspiration.

🦠 Pathogenicity

Dental/Oral infections: Periodontal disease, dental abscesses.
Lung abscesses: Especially in those with poor oral hygiene, aspiration, or alcohol misuse.
Human bite wounds: Soft tissue infections, cellulitis, septic arthritis from clenched-fist injuries.
Abdominal abscesses: Often as part of mixed anaerobic infections.
Endocarditis: Particularly in patients with prosthetic or damaged heart valves, linked with HACEK organisms.

🧪 Investigations

Cultures from pus, blood, or abscesses → colonies with pitting/corrosion on agar.
Gram stain shows slender Gram-negative rods.
May grow slowly; lab must be alerted if HACEK endocarditis is suspected.

⚠️ Resistance

Resistant to clindamycin and metronidazole ❌ (important because these are often given empirically for bite wounds).

💊 Sensitivities

Usually sensitive to:

Penicillins (ampicillin, amoxicillin).
Cephalosporins.
Tetracyclines.
Fluoroquinolones.

🛠️ Management

Human bite/clenched-fist injuries: Immediate wound irrigation and prophylaxis with co-amoxiclav (covers Eikenella + anaerobes).
Abscesses: Drainage + antibiotics.
Endocarditis: Requires prolonged IV antibiotics; consult microbiology.
Emphasise wound care and early intervention to prevent complications (e.g., septic arthritis, osteomyelitis).

📌 Key Exam Pearls

Eikenella is part of the HACEK group → think of it in cases of culture-negative endocarditis.
Not covered by metronidazole or clindamycin – exam favourite trick.
Commonly linked to human bites and fist injuries → always ask about mechanism in OSCEs.
Co-amoxiclav is the empirical antibiotic of choice in the UK for bite wounds.

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Eikenella corrodens

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