HACEK organisms

HACEK bacteria are a group of fastidious (has complex or particular nutritional requirements) G-bacteria that are among the uncommon causative agents of infective 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. HACEK organisms are a common component of the human microbiota residing in the oropharyngeal region. Bacteria were originally grouped together because they were thought to be important causative agents of infective endocarditis, but recent studies have shown that they are responsible for only 1.4-3.0% of 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, taxonomic rearrangement has changed the letter A to Aggregatibacter spp. and the letter H to Haemophillus spp. Some medical literature uses the older classification of HACEK group organisms, but recent publications respect the new classification.

List of organisms of the HACEK group

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

Features and identification

All these organisms are part of the normal oropharyngeal flora.

They grow slowly when cultured (up to 14 days), prefer an atmosphere with elevated CO2 tension, and share an increased capacity to induce endocarditis, especially in young children. Collectively, they are responsible for 5-10% of infective endocarditis cases involving native valve involvement. They are also among the most common Gram-negative agents of endocarditis among people who do not inject drugs.

Bývaly častým případem kultivačně neprokázané endokarditidy. Negativní kultivace se vztahuje k neschopnosti vytvořit kolonii na běžných agarových plotnách, jelikož tyto bakterie jsou náročné na kultivaci a vyžadují specifické nutrienty.

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

Treatment

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).