Nonenterococcal Group-D Streptococcal Endocarditis Caused by Streptococcus bovis

Streptococcal endocarditis has classically been divided into two distinct etiologic categories, the viridans group and the enterococci, the latter containing the group-D antigen. Enterococcal endocarditis requires a more prolonged multidrug therapeutic regimen than infection caused by the viridans group organisms. The group-D streptococci include two nonenterococcal species, Streptococcus bovis and S. equinus, which may be mistaken for enterococci in the clinical laboratory; however, S. bovis is readily distinguished from the enterococci by screening with bile-esculin hydrolysis and growth in 6.5% NaCl broth. Our clinical and in-vitro data indicate that patients with endocarditis caused by S. bovis or the enterococci share common gastrointestinal and genitourinary disease antecedents, but therapeutically and prognostically S. bovis endocarditis more closely resembles infection with the viridans group organisms. Reports of endocarditis caused by penicillin-sensitive "enterococci" were probably unrecognized examples of S. bovis infection, which warrants recognition as a separate category of streptococcal endocarditis.