Culture-negative bacterial endocarditis may be attributed to fastidious microorganisms, prior institution of antibiotic treatment, or both. We describe a case of culture-negative endocarditis in which a modified Steiner stain revealed bacterial structures in the resected heart valve material. Prompted by this finding, broad-range polymerase chain reaction (PCR) amplification of small-subunit ribosomal DNA (16S rDNA) was performed, and Cardiobacterium hominis sequences were detected. This case demonstrates the usefulness of both the Steiner stain and broad-range direct molecular amplification as supplemental diagnostic tools in identification of otherwise unexplained infections.
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Aortic valve tissue specimen from a 48-year-old man with culture-negative endocarditis. Pleomorphic argyrophilic rods and filaments are seen in panel A and clusters of bacilli in panel B (modified Steiner stain, original magnification ×1000).
Agarose gel electrophoresis of polymerase chain reaction (PCR) products. Twenty-six thermal cycles with primers 516F and 806R were performed. The M lanes indicate molecular-weight markers; lane 1, 5-µL heart valve digestion product used as PCR template; lane 2, 0.5-µL heart valve digestion product; lane 3, sterile water processed in a manner similar to the heart valve specimen (digestion control); lane 4, sterile water as template (negative PCR control); lane 5, Escherichia coli DNA (equivalent to 500 recombinant ribsomal RNA gene copies, positive PCR control); and bp, base pairs.
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