Taxonomy
Family: Neisseriaceae

HACEK
The HACEK organisms are a group of fastidious Gram-negative bacteria that are an unusual cause of infective endocarditis, which is an inflammation of the heart due to bacterial infection.
HACEK is an abbreviation of the initials of the genera of this group of bacteria:
Haemophilus aphrophilus (Aggregatibacter aphrophilus)
Aggregatibacter actinomycetemcomitans (previously Actinobacillus)
Cardiobacterium hominis
Eikenella corrodens
Kingella kingae.
The HACEK organisms are a normal part of the human microbiota, living in the oral-pharyngeal region.

The bacteria were originally grouped because they were thought to be a significant cause of infective endocarditis, but recent research has shown that they are rare and only responsible for 1.4–3.0% of all cases of this disease.

Natural habitats
The oral cavity and nasopharynx but possibly also the gastrointestinal and urogenital tract of humans and some mammals, from which it can be transmitted via saliva (bytes, syringes) to other individuals.

Clinical significans
They are associated with periodonitis, infections of the upper respiratory tract, pleura and lungs, abdomen, joints, bones, wounds (e.g, from a human bite), endocarditis, and rarely other infections, such as noma.

Risk factors are dental manipulations and intravenous drug abuse.