Endocarditis due to rare and fastidious bacteria

Abstract

The etiologic diagnosis of infective endocarditis is easily made in the presence of continuous bacteremia with gram-positive cocci. However, the blood culture may contain a bacterium rarely associated with endocarditis, such as Lactobacillus spp., Klebsiella spp., or nontoxigenic Corynebacterium, Salmonella, Gemella, Campylobacter, Aeromonas, Yersinia, Nocardia, Pasteurella, Listeria, or Erysipelothrix spp., that requires further investigation to establish the relationship with endocarditis, or the blood culture may be uninformative despite a supportive clinical evaluation. In the latter case, the etiologic agents are either fastidious extracellular or intracellular bacteria. Fastidious extracellular bacteria such as Abiotrophia, HACEK group bacteria, Clostridium, Brucella, Legionella, Mycobacterium, and Bartonella spp. need supplemented media, prolonged incubation time, and special culture conditions. Intracellular bacteria such as Coxiella burnetii cannot be isolated routinely. The two most prevalent etiologic agents of culture-negative endocarditis are C. burnetti and Bartonella spp. Their diagnosis is usually carried out serologically. A systemic pathologic examination of excised heart valves including periodic acid-Schiff (PAS) staining and molecular methods has allowed the identification of Whipple's bacillus endocarditis. Pathologic examination of the valve using special staining, such as Warthin-Starry, Gimenez, and PAS, and broad-spectrum PCR should be performed systematically when no etiologic diagnosis is evident through routine laboratory evaluation.

FIG. 1

Probable bacterial etiology of endocarditis depending on the patient history and epidemiologic situation. IVDU/IVDA, intravenous drug user/abusers.

FIG. 2

Abiotrophia spp. (formerly known as nutritionally deficient streptococci) showing satellite growth with Staphylococcus aureus. Photo courtesy of B. La Scola (Unité des Rickettsies, Marseilles, France).

FIG. 3

Whipple's disease endocarditis showing foamy PAS-positive macrophages (arrow). Magnification, ×1,000. Photo courtesy of H. Lepidi (Unité des Rickettsies, Marseilles, France).

FIG. 4

Warthin-Starry silver stain of a Bartonella quintana-infected valve. Note the cluster of bacteria in black within the vegetation. Magnification, ×100. Photo courtesy of H. Lepidi.

FIG. 5

Immunohistochemical demonstration of Coxiella burnetii in a heart valve of a patient with Q fever endocarditis. Magnification, ×600. Immumoalkaline phophatase staining was used.

FIG. 6

Phylogeny of the representative members of the α2 group of proteobacteria and location of Bartonella spp. based on analysis of the 16S rRNA sequence by the neighbor-joining method.

FIG. 7

Phylogeny of the HACEK group bacteria based on analysis of the 16S rRNA sequence by the neighbor-joining method.

FIG. 8

Phylogeny of Abiotrophia spp. (formerly known as nutritionally deficient streptococci) based on analysis of the 16S rRNA sequence by the neighbor-joining method.