HACEK group bacteria

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HACEK bacteria are a group of demanding G- bacteria, which are among the unusual causes of infectious endocarditis inflammatory heart disease due to infection).

HACEK is an abbreviation of the initials of the genera of bacteria belonging to this group: Haemophilus, Aggregatibacter (originally Actinobacillus), Cardiobacterium, Eikenella, Kingella. HACEK organisms are a common part of the human microbiota located in the oropharyngeal region. The bacteria were originally grouped because they were thought to be significant causes of infectious endocarditis, but recent research has shown that they are responsible for only 1,4–3,0% of infectious endocarditis.

Individual organisms

The HACEK group originally referred to Haemophilus parainfluenzae, Haemophilus aphrophilus, Actinobacillus actinomycetemcomitans, Cardiobacterium hominis, Eikenella corrodens, and Kingella kingae.

However, the taxonomic rearrangement changed the letter A to Aggregatibacter spp. and the letter H to Haemophillus spp.. Some medical literature uses an older classification of HACEK organisms, but recent publications respect the new classification.

List of HACEK organisms:

Genus Haemophillus:

• Haemophilus haemolyticus
• Haemophilus influenzae – The incidence of endocarditis caused by H. influenzae has decreased since the vaccine was placed on the market
• Haemophilus parahaemolyticus
• Haemophilus parainfluenzae

Aggregatibacter:

• Aggregatibacter actinomycetemcomitans (originally Actinobacillus actinomycetemcomitans)
• Aggregatibacter aphrophilus (originally Haemophilus aphrophilus)
• Aggregatibacter paraphrophilus (originally Haemophilus aphrophilus)
• Aggregatibacter segnis

Cardiobacterium

• Cardiobacterium hominis – the most common species in the genus Cardiobacterium
• Cardiobacterium valvarum

Eikenella

• Eikenella corrodens

Kingella

• Kingella denitrificans
• Kingella kingae – the most common species in the genus Kingella

Properties and identification

All of these organisms are part of the normal oropharyngeal flora.

They grow slowly during cultivation (up to 14 days, they prefer an atmosphere with increased CO₂ tension and share an increased capacity to induce endocarditis, especially in young children. Together, they are responsible for 5-10% of infectious endocarditis cases involving native valve involvement. At the same time, it is one of the most common Gram-negative causes of endocarditis among people who do not use intravenous drugs.

They were often a case of cultivation-unproven endocarditis. Negative cultivation refers to the inability to form a colony on conventional agar plates, as these bacteria are difficult to cultivate and require specific nutrients.

In addition to valvular infections in the heart, these bacteria can cause other diseases such as bacteremia, abscess, peritonitis, otitis media, conjunctivitis, pneumonia, arthritis, osteomyelitis and periodontal infections.

Therapy

The drug of choice for HACEK organisms in endocarditis is 3rd generation cephalosporin and β-lactam antibiotic Ceftriaxon. Another therapeutic option is Ampicilin combined with low doses of gentamicin (aminoglycosid).

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