Haemophilus species have been isolated from brain abscesses, meningitis, endocarditis, otitis media, sinusitis, epiglottitis, hepatic abscesses, intra-abdominal infections, pneumonia, necrotizing fasciitis, septic arthritis, osteomyelitis, postoperative surgical infections, and urinary tract infections (UTIs). 11 For the purposes of this review, all of the HACEK-causing species formally in the Haemophilus genus will be referred to by the genus name. H aphrophilus, H paraphrophilus, and H segnis recently were classified, along with A actinomycetemcomitans, into the genus Aggregatibacter. Haemophilus Species: Haemophilus species apart from the HACEK group include aphrophilus, haemolyticus, parahaemolyticus, parainfluenzae, paraphrophilus, and segnis. It is important to remember that there are other potential culture-negative species besides HACEK organisms, such as Legionella species, Bartonella species, Brucella species, and other fastidious pathogens. 1 With the advent of improved culture media and automated culture systems, prolonged incubation may no longer be necessary a 3- to 7-day incubation period may suffice. 8 Typically, HACEK organisms grow slowly and are subject to extended incubation periods of 7 to 21 days. 8,9 They grow well on nonspecific culture media rather than specialized agars like MacConkey’s agar, a growth medium for gram-negative bacteria. ![]() To grow, HACEK organisms need an atmosphere enriched with carbon dioxide. 4 This article will briefly review the HACEK pathogens, resulting infections, and common treatment approaches. 1,5-7 Rarely, HACEK organisms may cause severe systemic infections. 4 HACEK organisms are most often associated with infective endocarditis, accounting for up to 10% of cases. 2,3 These organisms commonly colonize the human oropharynx as normal, indigenous flora that could cause mouth infections. 1 The HACEK organisms include H aemophilus species, A ggregatibacter actinomycetemcomitans, C ardiobacterium hominis, E ikenella corrodens, and K ingella kingae. HACEK is an acronym for a group of organisms that are small, fastidious gram-negative bacilli.
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