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.[1] HACEK is an abbreviation of the initials of the genera of this group of bacteria: Haemophilus, Aggregatibacter (previously Actinobacillus), Cardiobacterium, Eikenella, Kingella.[1] The HACEK organisms are a normal part of the human microbiota, living in the oral-pharyngeal region.[2]
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.[1]