Infective endocarditis associated with cell wall-deficient bacteria. Electron microscopic findings in four cases.

Although cell wall-deficient bacteria have been isolated in vitro from cases of endocarditis, no pathogenic role has been established for these forms in human disease. One criterion difficult to satisfy is the demonstration of these variants in human tissue, and electron microscopic documentation has not been reported. Cardiac valvular vegetations from four cases of endocarditis were examined by electron microscopy because of unusual histologic features of minimal inflammation and organization and small organisms that stained poorly by Gram stain. Although cell wall-complete bacteria were identified in the specimens, each showed the presence of cell wall-deficient forms within the vegetations; these variants predominated in three cases. Since manifestations of infective endocarditis were present in three cases and conventional cultures were negative, the evidence indirectly suggests a pathogenic role for these aberrant bacteria in human disease.