HACEK organism

Group of Gram-negative bacteria associated with endocarditis

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colspan=2 style="text-align: center; background-color: transparent" | HACEK organisms
colspan=2 style="min-width:15em; text-align: center; background-color: transparent" | Scientific classification
Missing taxonomy template ([//en.wikipedia.org/w/index.php?action=edit&title=Template:taxonomy/HACEK+organism&preload=Template:Taxonomy/preload fix]):	HACEK organism
colspan=2 style="text-align: center; background-color: transparent" | Genera
Haemophilus Aggregatibacter Cardiobacterium Eikenella Kingella

HACEK organisms are a group of Gram-negative bacteria that are part of the normal flora of the human oropharynx but are known for their association with endocarditis, an infection of the inner lining of the heart. The acronym "HACEK" stands for the genera Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, and Kingella.

Characteristics

HACEK organisms are fastidious, meaning they require specific nutrients and conditions to grow in laboratory cultures. They are capnophilic, thriving in environments with higher levels of carbon dioxide. These bacteria are slow-growing, which can complicate their detection in clinical settings.

Haemophilus

Haemophilus species, particularly Haemophilus parainfluenzae, are part of the HACEK group. They are small, pleomorphic, Gram-negative coccobacilli that require factors V (NAD) and X (hemin) for growth.

Aggregatibacter

Aggregatibacter includes species such as Aggregatibacter actinomycetemcomitans, which is associated with periodontal disease and endocarditis. These bacteria are small, non-motile, and can form star-shaped colonies on agar.

Cardiobacterium

Cardiobacterium hominis is the primary species in this genus associated with endocarditis. It is a Gram-negative rod that can exhibit a "rosette" formation in cultures.

Eikenella

Eikenella corrodens is known for its ability to "pit" or "corrode" agar surfaces. It is part of the normal flora of the human mouth and can cause infections following human bites or fistfights.

Kingella

Kingella kingae is increasingly recognized as a cause of pediatric osteoarticular infections and endocarditis. It is a short, plump, Gram-negative rod that can be mistaken for Neisseria species.

Clinical Significance

HACEK organisms are a rare cause of infective endocarditis, accounting for approximately 3% of all cases. They are more commonly associated with subacute presentations of the disease. Due to their fastidious nature, they may not be detected in routine blood cultures, requiring prolonged incubation or specialized media.

Diagnosis and Treatment

Diagnosis of HACEK-related infections often involves prolonged blood culture incubation and the use of molecular techniques such as PCR for identification. Treatment typically involves prolonged courses of antibiotics, with ceftriaxone being a common choice due to its efficacy and ease of administration.

Also see

• Endocarditis
• Gram-negative bacteria
• Infective endocarditis
• Bacterial culture