The HACEK organisms are:

Haemophilus species (H. aphrophilus, H. paraphrophilus, H. parainfluenzae) Actinobacillus actinomycetemcomitans

Cardiobacterium hominis

Eikenella corrodens

Kingella

These are gram negative bacilli which are responsible for 5-10% of cases of infective endocarditis (IE) involving native valves and are the most common cause of gram- negative endocarditis among persons who do not abuse intravenous drugs.