TAILIEUCHUNG - Chapter 140. Infections Due to the HACEK Group and Miscellaneous GramNegative Bacteria

HACEK organisms are a group of fastidious, slow-growing, gram-negative bacteria whose growth requires an atmosphere of carbon dioxide. Species belonging to this group include several Haemophilus species, Actinobacillus actinomycetemcomitans, Cardiobacterium hominis, Eikenella corrodens, and Kingella kingae. HACEK bacteria normally reside in the oral cavity and have been associated with local infections in the mouth. They are also known to cause severe systemic infections— most often bacterial endocarditis, which can develop on either native or prosthetic valves (Chap. 118). HACEK Endocarditis In large series, up to 3% of cases of infective endocarditis are attributable to HACEK organisms, most often A | Chapter 140. Infections Due to the HACEK Group and Miscellaneous Gram- Negative Bacteria HACEK organisms are a group of fastidious slow-growing gram-negative bacteria whose growth requires an atmosphere of carbon dioxide. Species belonging to this group include several Haemophilus species Actinobacillus actinomycetemcomitans Cardiobacterium hominis Eikenella corrodens and Kingella kingae. HACEK bacteria normally reside in the oral cavity and have been associated with local infections in the mouth. They are also known to cause severe systemic infections most often bacterial endocarditis which can develop on either native or prosthetic valves Chap. 118 . HACEK Endocarditis In large series up to 3 of cases of infective endocarditis are attributable to HACEK organisms most often A. actinomycetemcomitans Haemophilus species and C. hominis. The clinical course of HACEK endocarditis tends to be subacute however embolization is common. The overall prevalence of major emboli associated with HACEK endocarditis ranges from 28 to 71 in different series. On echocardiography valvular vegetations are seen in up to 85 of patients. The vegetations are frequently large although vegetation size has not been directly correlated with the risk of embolization. Cultures of blood from patients with suspected HACEK endocarditis may require up to 30 days to become positive and the microbiology laboratory should be alerted when a HACEK organism is being considered. However most cultures that ultimately yield a HACEK organism become positive within the first week especially with improved culture systems such as BACTEC. In addition polymerase chain reaction techniques are facilitating the diagnosis of HACEK infections. Because of the organisms slow growth antimicrobial testing may be difficult and p-lactamase production may not be detected. E-test methodology may increase the accuracy of susceptibility testing. Haemophilus Species Haemophilus species are differentiated by their in vitro growth

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