Fastidiosos

Grupo HACEK (Haemophilus/Aggregatibacter, Kingella, Eikenella)

Fastidious Gram-negative coccobacilli

Identification & Growth

Identification

Slow, CO2-dependent growth; variable oxidase reaction
Eikenella pits the agar and has a bleach-like odour

Growth Conditions

Chocolate agar, 35–37 °C, 5% CO2, up to 5 days — do not discard blood cultures early

Clinical Significance

Subacute native-valve endocarditis, oral abscess, human-bite infection

Intrinsic Resistance

Eikenella is resistant to clindamycin and aminoglycosides

Bench Alerts

Culture-negative endocarditis blood cultures require prolonged incubation
Ceftriaxone is the backbone of treatment

Clinical Notes

Clinical presentations

Subacute infective endocarditis of native or prosthetic valves, with large vegetations and peripheral embolization.
Kingella kingae is a relevant cause of septic arthritis and osteomyelitis in children under 4 years.
Eikenella corrodens in head and neck abscesses and in human-bite or clenched-fist injuries.

Specimens and collection

Three blood-culture sets from separate sites before antimicrobials, with adequate volume per bottle.
Keep bottles for the standard incubation period of the automated system: with current media, routine extended incubation is unnecessary.
In paediatric arthritis, inoculate synovial fluid into a blood-culture bottle and add K. kingae PCR, which greatly increases sensitivity.

Epidemiology and at-risk populations

They belong to the oropharyngeal microbiota; the usual entry point is dental or oral mucosal.
They account for a small fraction of endocarditis cases but a notable share of initially culture-negative endocarditis.
Increased risk with prior valve disease, prosthetic valves, congenital heart disease and poor oral hygiene.

Resistance and therapeutic implications

Some strains produce beta-lactamase: ampicillin alone is not a reliable empirical option.
Ceftriaxone is the regimen of choice in HACEK endocarditis guidelines, with ampicillin-sulbactam or a fluoroquinolone as alternatives.
All HACEK organisms are intrinsically resistant to glycopeptides, clindamycin and polymyxins — do not report these classes as options.

Bench and reporting notes

Fastidious organisms: they require chocolate agar and a 5% CO2 atmosphere, growing slowly with small colonies at 48–72 h.
Eikenella pits the agar and smells of bleach; Aggregatibacter forms adherent colonies with a star-shaped centre.
Test susceptibility only by MIC in medium suitable for fastidious organisms and state the method in the report.

Sources

Educational decision-support content. It does not replace laboratory validation, current guidelines or review by the responsible professional.

FAQ: Frequently Asked Questions

How to identify Grupo HACEK (Haemophilus/Aggregatibacter, Kingella, Eikenella) in the lab?

Grupo HACEK (Haemophilus/Aggregatibacter, Kingella, Eikenella) is identified through slow, co2-dependent growth; variable oxidase reaction, eikenella pits the agar and has a bleach-like odour.

What are the intrinsic resistances of Grupo HACEK (Haemophilus/Aggregatibacter, Kingella, Eikenella)?

This organism is naturally resistant to eikenella is resistant to clindamycin and aminoglycosides. These drugs should not be reported as susceptible.

Where is Grupo HACEK (Haemophilus/Aggregatibacter, Kingella, Eikenella) commonly found?

It is typically associated with subacute native-valve endocarditis, oral abscess, human-bite infection.

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