TheHACEK organisms are a group offastidiousGram-negativebacteria that are an unusual cause ofinfective endocarditis, which is an inflammation of the heart due to bacterial infection.[1] HACEK is an abbreviation of the initials of thegenera of this group of bacteria:Haemophilus,Aggregatibacter (previouslyActinobacillus),Cardiobacterium,Eikenella,Kingella.[1] The HACEK organisms are a normal part of thehuman microbiota, living in theoral-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]
HACEK originally referred toHaemophilus parainfluenzae,Haemophilus aphrophilus,Actinobacillus actinomycetemcomitans,Cardiobacterium hominis,Eikenella corrodens, andKingella kingae. However, taxonomic rearrangements have changed the A toAggregatibacter species and theH toHaemophilus species to reflect the recategorization and novel identification of many of the species in thesegenera.[1] Some reviews of medical literature on HACEK organisms use the older classification,[3] but recent papers are using the new classification.[4][5][6]
A list of HACEK organisms:
All of these organisms are part of the normal oropharyngeal flora, which grow slowly (up to 14 days), prefer a carbon dioxide–enriched atmosphere, and share an enhanced capacity to produce endocardial infections, especially in young children. Collectively, they account for 5–10% of cases of infectiveendocarditis involving native valves and are the most common Gram-negative cause of endocarditis among people who do not use drugs intravenously. They have been a frequent cause of culture-negative endocarditis. Culture-negative refers to an inability to produce a colony on regular agar plates because these bacteria are fastidious (require a specific nutrient).
In addition to valvular infections in the heart, they can also produce other infections, such asbacteremia,abscess,peritonitis,otitis media,conjunctivitis,pneumonia,arthritis,osteomyelitis, andperiodontal infections.
The treatment of choice for HACEK organisms in endocarditis is the third-generationcephalosporin andβ-Lactam antibioticceftriaxone.Ampicillin (apenicillin), combined with low-dosegentamicin (anaminoglycoside) is another therapeutic option.[7]