The bacteria were originally grouped because they were thought to be a significant cause of 
- Organisms 1
- Presentation 2
- Treatment 3
- References 4
HACEK originally referred to
The treatment of choice for HACEK organisms in endocarditis is ceftriaxone, a third generation cephalosporin and a β-Lactam antibiotic (as are the penicillins). Ampicillin (a penicillin) and low-dose gentamicin (an aminoglycoside) is another therapeutic option.
In addition to valvular infections in the heart, they can also produce other infections such as bacteremia, abscess, peritonitis, otitis media, conjunctivitis, pneumonia, arthritis, osteomyelitis, and periodontal infections.
All of these organisms are part of the normal oropharyngeal flora, which grow slowly (up to 14 days), prefer a carbon dioxide–enriched atmosphere, and share an enhanced capacity to produce endocardial infections, especially in young children. Collectively 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. They have been a frequent cause of culture-negative endocarditis. Culture negative refers to an inability to produce a colony on regular agar plates; this is because these bacteria are fastidious (requiring a specific nutrient).
- Haemophilus species
A list of HACEK organisms:
 but recent papers are using the new classification.