The HACEK group refers to a collection of bacteria that are associated with endocarditis (infection of the heart's inner lining). The acronym HACEK stands for the following bacteria:
H: Haemophilus parainfluenzae
A: Aggregatibacter species
C: Cardiobacterium hominis
E: Eikenella corrodens
K: Kingella kingae
These bacteria are fastidious (difficult to culture) and are part of the normal flora of the human mouth and upper respiratory tract, but they can cause infections, especially in individuals with underlying heart conditions or compromised immune systems.