HACEK organisms

HACEK organisms

HACEK organisms are a group of fastidious Gram-negative bacteria that are part of the normal flora of the oropharynx but are clinically important because they can cause infective endocarditis (especially culture-negative cases).

🔤 HACEK acronym

Each letter represents a genus:

• H – Haemophilus species(e.g., Haemophilus parainfluenzae, Haemophilus aphrophilus → now reclassified)

• A – Aggregatibacter species(e.g., Aggregatibacter actinomycetemcomitans)

• C – Cardiobacterium hominis

• E – Eikenella corrodens

• K – Kingella species(e.g., Kingella kingae)

🧬 Key characteristics

• Gram-negative bacilli/coccobacilli

• Fastidious (require enriched media, slow growing)

• Normal oral flora

• Often associated with subacute infective endocarditis

🫀 Clinical relevance

• Cause culture-negative endocarditis (slow growth delays detection)

• Can follow dental procedures or poor oral hygiene

• May also cause:

  • Periodontal infections

  • Abscesses

  • Bacteremia

💊 Treatment

• Typically sensitive to:

  • Ceftriaxone (drug of choice)

  • Fluoroquinolones (alternative)

• Some produce β-lactamase, so penicillin alone may not always work