The HACEK organisms are a group of

fastidious A fastidious organism is any organism that has complex or particular nutritional requirements. In other words, a fastidious organism will only grow when specific nutrients are included in its medium. The more restrictive term fastidious microorgan ...

Gram-negative Gram-negative bacteria are bacteria that, unlike gram-positive bacteria, do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. Their defining characteristic is that their cell envelope consists ...

bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

that are an unusual cause of

infective endocarditis Infective endocarditis is an infection of the inner surface of the heart (endocardium), usually the heart valve, valves. Signs and symptoms may include fever, petechia, small areas of bleeding into the skin, heart murmur, feeling tired, and anem ...

, which is an inflammation of the heart due to bacterial infection. HACEK is an abbreviation of the initials of the

genera Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...

of this group of bacteria: ''

Haemophilus ''Haemophilus'' is a genus of Gram-negative, pleomorphic, coccobacilli bacteria belonging to the family Pasteurellaceae. While ''Haemophilus'' bacteria are typically small coccobacilli, they are categorized as pleomorphic bacteria because of ...

'', '' Aggregatibacter'' (previously '' Actinobacillus''), ''

Cardiobacterium ''Cardiobacterium'' is a genus of bacteria in the family Cardiobacteriaceae. These Gram-negative bacillus ''Bacillus'', from Latin "bacillus", meaning "little staff, wand", is a genus of Gram-positive, rod-shaped bacteria, a member of the p ...

'', ''

Eikenella The Neisseriaceae are a family of ''Pseudomonadota'', within the ''Neisseriales'' order of ''Betaproteobacteria''. While many organisms in the family are mammalian commensals or part of the normal flora, the genus ''Neisseria'' includes two impor ...

'', ''

Kingella ''Kingella'' is a genus of bacteria of the family Neisseriaceae. It belongs to the HACEK group of fastidious Gram-negative bacteria that tend to cause endocarditis. ''Kingella kingae'' is its type species. Species As of 2021, five species belo ...

''. The HACEK organisms are a normal part of the

human microbiota Human microbiota are microorganisms (bacteria, viruses, fungi and archaea) found in a specific environment. They can be found in the stomach, intestines, skin, genitals and other parts of the body. Various body parts have diverse microorganisms. S ...

, living in the

oral The word oral may refer to: Relating to the mouth * Relating to the mouth, the first portion of the alimentary canal that primarily receives food and liquid **Oral administration of medicines ** Oral examination (also known as an oral exam or ora ...

- pharyngeal region. 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.

Organisms

HACEK originally referred to ''

Haemophilus parainfluenzae ''Haemophilus parainfluenzae'' is a species of'' Haemophilus''. It is one of the HACEK organisms. ''H. parainfluenzae'' is an opportunistic pathogen that has been associated with endocarditis, bronchitis, otitis, conjunctivitis, pneumonia, a ...

'', '' Haemophilus aphrophilus'', '' Actinobacillus actinomycetemcomitans'', ''

Cardiobacterium hominis ''Cardiobacterium hominis'' /ˌkɑːrdiəʊbækˈtɪəriəm ˈhɒmɪnɪs/ (KAR-dee-oh-bak-TEER-ee-um HOM-i-nis) is a microaerophilic, pleomorphic, fastidious, Gram-negative bacterium part of the Cardiobacteriaceae family and the HACEK group. ...

'', '' Eikenella corrodens'', and ''

Kingella kingae ''Kingella kingae'' is a species of Gram-negative facultative anaerobic β-hemolytic coccobacilli. First isolated in 1960 by Elizabeth O. King, it was not recognized as a significant cause of infection in young children until the 1990s, when c ...

''. However, taxonomic rearrangements have changed the A to '' Aggregatibacter'' species and the H to ''

'' species to reflect the recategorization and novel identification of many of the species in these

. Some reviews of medical literature on HACEK organisms use the older classification, but recent papers are using the new classification. A list of HACEK organisms: *''

''species **'' Haemophilus haemolyticus'' **''

Haemophilus influenzae ''Haemophilus influenzae'' (formerly called Pfeiffer's bacillus or ''Bacillus influenzae'') is a Gram-negative, Motility, non-motile, Coccobacillus, coccobacillary, facultative anaerobic organism, facultatively anaerobic, Capnophile, capnophili ...

'': The incidence of endocarditis due to ''H. influenzae'' declined after the introduction of the

Hib vaccine The ''Haemophilus influenzae'' type B vaccine, also known as Hib vaccine, is a vaccine used to prevent ''Haemophilus influenzae'' type b (Hib) infection. In countries that include it as a vaccination schedule, routine vaccine, rates of severe ...

. **''

Haemophilus parahaemolyticus ''Haemophilus'' is a genus of Gram-negative, pleomorphic, coccobacilli bacteria belonging to the family Pasteurellaceae. While ''Haemophilus'' bacteria are typically small coccobacilli, they are categorized as pleomorphic bacteria because of ...

'' **''

'' *'' Aggregatibacter'' **''

Aggregatibacter actinomycetemcomitans ''Aggregatibacter actinomycetemcomitans'' is a Gram-negative, facultative anaerobe, nonmotile bacterium that is often found in association with localized aggressive periodontitis, a severe infection of the periodontium. It is also suspected to b ...

'' (previously '' Actinobacillus actinomycetemcomitans'') **'' Aggregatibacter aphrophilus'' (previously '' Haemophilus aphrophilus'') **'' Aggregatibacter paraphrophilus'' (previously '' Haemophilus aphrophilus'') **'' Aggregatibacter segnis'' *''

'' **''

'': This is the most common species in the genus ''Cardiobacterium''. **''

Cardiobacterium valvarum ''Cardiobacterium valvarum'' is a Gram-negative species of bacteria belonging to the Cardiobacterium genus. It belongs to the HACEK group of fastidious bacteria that are present in normal oropharyngeal flora and can develop into infective endocard ...

'' *''

'' **'' Eikenella corrodens'' *''

'' **'' Kingella denitrificans'' **''

'': This is the most common species in the genus ''Kingella''.

Presentation

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 infective

endocarditis Endocarditis is an inflammation of the inner layer of the heart, the endocardium. It usually involves the heart valves. Other structures that may be involved include the interventricular septum, the chordae tendineae, the mural endocardium, o ...

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 as

bacteremia Bloodstream infections (BSIs) are infections of blood caused by blood-borne pathogens. The detection of microbes in the blood (most commonly accomplished by blood cultures) is always abnormal. A bloodstream infection is different from sepsis, wh ...

abscess An abscess is a collection of pus that has built up within the tissue of the body, usually caused by bacterial infection. Signs and symptoms of abscesses include redness, pain, warmth, and swelling. The swelling may feel fluid-filled when pre ...

peritonitis Peritonitis is inflammation of the localized or generalized peritoneum, the lining of the inner wall of the abdomen and covering of the abdominal organs. Symptoms may include severe pain, swelling of the abdomen, fever, or weight loss. One pa ...

otitis media Otitis media is a group of Inflammation, inflammatory diseases of the middle ear. One of the two main types is acute otitis media (AOM), an infection of rapid onset that usually presents with ear pain. In young children this may result in pullin ...

conjunctivitis Conjunctivitis, also known as pink eye or Madras eye, is inflammation of the conjunctiva, the thin, clear layer that covers the white surface of the eye and the inner eyelid. It makes the eye appear pink or reddish. Pain, burning, scratchiness ...

pneumonia Pneumonia is an Inflammation, inflammatory condition of the lung primarily affecting the small air sacs known as Pulmonary alveolus, alveoli. Symptoms typically include some combination of Cough#Classification, productive or dry cough, ches ...

arthritis Arthritis is a general medical term used to describe a disorder that affects joints. Symptoms generally include joint pain and stiffness. Other symptoms may include redness, warmth, Joint effusion, swelling, and decreased range of motion of ...

osteomyelitis Osteomyelitis (OM) is the infectious inflammation of bone marrow. Symptoms may include pain in a specific bone with overlying redness, fever, and weakness. The feet, spine, and hips are the most commonly involved bones in adults. The cause is ...

, and periodontal infections.

Treatment

The treatment of choice for HACEK organisms in endocarditis is the third-generation

cephalosporin The cephalosporins (sg. ) are a class of β-lactam antibiotics originally derived from the fungus '' Acremonium'', which was previously known as ''Cephalosporium''. Together with cephamycins, they constitute a subgroup of β-lactam antibio ...

and β-Lactam antibiotic

ceftriaxone Ceftriaxone, sold under the brand name Rocephin, is a third-generation cephalosporin antibiotic used for the treatment of a number of bacterial infections. These include middle ear infections, endocarditis, meningitis, pneumonia, bone and joi ...

Ampicillin Ampicillin is an antibiotic belonging to the aminopenicillin class of the penicillin family. The drug is used to prevent and treat several bacterial infections, such as respiratory tract infections, urinary tract infections, meningitis, s ...

penicillin Penicillins (P, PCN or PEN) are a group of beta-lactam antibiotic, β-lactam antibiotics originally obtained from ''Penicillium'' Mold (fungus), moulds, principally ''Penicillium chrysogenum, P. chrysogenum'' and ''Penicillium rubens, P. ru ...

), combined with low-dose

gentamicin Gentamicin is an aminoglycoside antibiotic used to treat several types of bacterial infections. This may include bone infections, endocarditis, pelvic inflammatory disease, meningitis, pneumonia, urinary tract infections, and sepsis amo ...

(an

aminoglycoside Aminoglycoside is a medicinal and bacteriologic category of traditional Gram-negative antibacterial medications that inhibit protein synthesis and contain as a portion of the molecule an amino-modified glycoside (sugar). The term can also refer ...

) is another therapeutic option.
eMedicine, HACEK organism infection. June 2005.

References

{{DEFAULTSORT:Hacek Endocarditis Bacteria Pathogenic bacteria