The HACEK group includes weakly virulent, gram-negative organisms that primarily cause endocarditis.
The HACEK group of nonmotile, gram-negative bacilli or coccobacilli contains a number of minimally pathogenic, slow-growing, fastidious genera. Their primary pathology is endocarditis in susceptible people; about 5% of endocarditis cases are due to this group, making them the most common causes of gram-negative bacilli endocarditis. The group consists of
Haemophilus sp (H. parainfluenza, H. aphrophilus, and H. paraphrophilus), which may cause respiratory infections or, less commonly, endocarditis
Aggregatibacter (formerly Actinobacillus) actinomycetemcomitans, which usually occurs with A. israelii in actinomycosis
Eikenella corrodens, which usually occurs in human bite wounds, endocarditis (often in IV drug users), brain and visceral abscesses, osteomyelitis, respiratory infections (including empyemas), uterine infections related to intrauterine devices, and mixed soft-tissue infections
Antibiotic sensitivities differ among species, so treatment should be directed by susceptibility testing. However, increasing beta-lactam resistance has made ceftriaxone and ampicillin/sulbactam the current antibiotics of choice.