HACEK organism
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Template:GCC
Overview
HACEK organisms is a group of fastidious, slow growing, pleomorphic Gram negative bacilli which form part of the oropharynx commensals and require enhanced carbon dioxide tension for recovery in culture. HACEK organisms account for about 3% of cases of endocarditis,[1] with an insidious onset and subacute course. HACEK refers to the initials of organisms including:
- Haemophilus parainfluenzae, Aggregatibacter aphrophilus (formerly Haemophilus aphrophilus and Haemophilus paraphrophilus)[2]
Pathophysiology
All of these organisms are part of the normal oropharyngeal flora which grow slowly, prefer a carbon dioxide–enriched atmosphere and share an enhanced capacity to produce endocardial infections, especially in young children.
In addition to valvular infections in the heart, these organisms can also produce other infections such as bacteremia, abscesses, peritonitis, otitis media, conjunctivitis, pneumonia, peritonitis, arthritis and osteomyelitis, and periodontal infections.
Epidemiology and Demographics
Collectivelly, they account for 5-10% of cases of infective endocarditis involving native valves and are the most common gram-negative cause of endocarditis among people who do not use IV drugs.
Diagnosis
Laboratory Studies
Given the fastidious growth requirements, HACEK bacteria are a recognized cause of culture-negative endocarditis. The organisms can be identified after subculture on 5 to 8% sheep blood and chocolate agar at 35 to 37°C for 48 to 72 h in an aerobic atmosphere containing 5 to 10% CO2. Biochemical properties are used to differentiate members of the HACEK group. However, biopatterns are affected by factors such as inoculum volume and the growth conditions, which prompts the utilization of molecular techniques such as 16S ribosomal RNA sequencing.
Treatment
The treatment of endocarditis caused by HACEK organisms should be based on antimicrobial susceptibility tests, including tests for β-lactamase ctivity. Since many of these organisms are slow growing, such tests can be problematic. Currently, third-generation cephalosporins, including cefotaxime or ceftriaxone, are the drugs of choice for treating endocarditis caused by the HACEK organisms.[3] Native-valve endocarditis should be treated for 4 weeks of antiobiotics, whereas prosthetic-valve endocarditis requires 6 weeks of therapy. HACEK endocarditis is associated with a favorable prognosis, with a cure rate of 82 to 87% of patients with medical treatment alone or associated with surgery.[4]
References
- ↑ Steckelberg JM, Melton LJ, Ilstrup DM, Rouse MS, Wilson WR (1990). "Influence of referral bias on the apparent clinical spectrum of infective endocarditis". Am. J. Med. 88 (6): 582–8. PMID 2346159. Unknown parameter
|month=ignored (help) - ↑ 2.0 2.1 Nørskov-Lauritsen N, Kilian M (2006). "Reclassification of Actinobacillus actinomycetemcomitans, Haemophilus aphrophilus, Haemophilus paraphrophilus and Haemophilus segnis as Aggregatibacter actinomycetemcomitans gen. nov., comb. nov., Aggregatibacter aphrophilus comb. nov. and Aggregatibacter segnis comb. nov., and emended description of Aggregatibacter aphrophilus to include V factor-dependent and V factor-independent isolates". Int. J. Syst. Evol. Microbiol. 56 (Pt 9): 2135–46. doi:10.1099/ijs.0.64207-0. PMID 16957111. Unknown parameter
|month=ignored (help) - ↑ Loscalzo, Joseph; Longo, Dan L.; Fauci, Anthony S.; Dennis L. Kasper; Hauser, Stephen L (2011). Harrison's Principles of Internal Medicine, 18th Edition. McGraw-Hill Professional. ISBN 0-07-174889-X.
- ↑ Berbari EF, Cockerill FR, Steckelberg JM (1997). "Infective endocarditis due to unusual or fastidious microorganisms". Mayo Clin. Proc. 72 (6): 532–42. doi:10.1016/S0025-6196(11)63302-8. PMID 9179137. Unknown parameter
|month=ignored (help)