Microbiology of Infective Endocarditis and Microbiologic Diagnosis

Abstract

The microbiology of infective endocarditis (IE) has evolved significantly over the last century. Previously a community-acquired disease affecting predominantly patients with rheumatic heart disease, IE is now being seen in new populations including IV drug users, patients with prosthetic valves, and patients infected through healthcare associated bacteremia. Improved blood culture technologies and non-culture laboratory methods have also resulted in a lower rate of culture-negative cases. Because of differing proportions of particular risk groups, the etiologic agents responsible for causing infective endocarditis vary significantly among continents, countries, regions within countries and even between different years in an individual hospital.

Blood culture remains the single most important investigation in a patient suspected of having infective endocarditis. If appropriately collected prior to antibiotic administration, blood cultures can be expected to yield growth of the causative organism in over 90 % of cases of infective endocarditis. Serologic testing can be useful in determining the cause of IE in true culture-negative cases, which are usually caused by organisms that are difficult to culture including Coxiella burnetti, Bartonella spp., Chlamydia spp. and Legionella species. In spite of limitations including the potential presence of PCR inhibitors in clinical samples and the possibility of sample to sample contamination, molecular amplification methods can be useful in establishing the cause of IE. To date, PCR methods have been applied with most success to surgically excised valve tissues.