HACEK organisms

These organisms can cause “culture negative endocarditis” meaning infection of the endocardium with vegetation formation despite blood cultures not showing evidence of bacteremia. The above organisms require special medium or prolonged incubation to be isolated. The most common causes of culture negative endocarditis are actually Streptococcus species in patients who already received antibiotic therapy (rendering the blood cultures negative) and fungi.

Haemophilus aphrophilus
Actinobacillus actinomycetemcomitans
Cardiobacterium hominis
Eikenella corrodens
Kingella kingae