HACEK organism

Definition and Classification
A HACEK organism is one of a set of slow-growing Gram negative bacteria that form a normal part of the human flora. They are a frequent cause of endocarditis in children.

The name is formed from their initials:


 * Haemophilus aphrophilus, Haemophilus parainfluenzae and Haemophilus paraphrophilus
 * Actinobacillus actinomycetemcomitans
 * Cardiobacterium hominis
 * Eikenella corrodens
 * Kingella kingae

Pathophysiology
All of these organisms are part of the normal oropharyngeal flora which grow slowly, prefer a carbon dioxide–enriched atmosphere and share an enhanced capacity to produce endocardial infections, especially in young children.

In addition to valvular infections in the heart, these organisms can also produce other infections such as bacteremia, abscesses, peritonitis, otitis media, conjunctivitis, pneumonia, peritonitis, arthritis and osteomyelitis, and periodontal infections.

Epidemiology and Demographics
Collectivelly, they account for 5-10% of cases of infective endocarditis involving native valves and are the most common gram-negative cause of endocarditis among people who do not use IV drugs.

Laboratory Studies
Because of their fastidious growth requirements, they have been a frequent cause of culture-negative endocarditis. Culture negative refers to its inability to produce a colony on regular agar plates, this is because they are fastidious (require a specific nutrient).

Treatment
The treatment of choice for HACEK organisms in endocarditis is ceftriaxone, a cephalosporin antibiotic. The dose is 2 g I.V. daily as a single dose for 4 weeks.