Treatment of Bacterial Endocarditis Caused by Penicillin-Sensitive Streptococci

In this issue, Robbins et al describe three cases of endocarditis due to Streptococcus mutans, one of the viridans streptococci (p 1171). They emphasize that, as with S bovis (a nonenterococcal group D streptococcus), S mutans can easily be mistaken for an enterococcus if the appropriate laboratory tests are not performed. Streptococcus mutans and S bovis are more susceptible to lower concentrations of multiple antibiotics, including penicillin, than are the enterococci. Streptococcus bovis endocarditis has been successfully treated with penicillin alone; however, Robbin's report represents the first published case of S mutans endocarditis treated in this manner. Many authors recommend treating endocarditis caused by streptococci that have a minimum inhibitory concentration (MIC) against penicillin of 0.2 μg/ml or less with penicillin alone. The more resistant viridans organisms and the enterococci require an aminoglycoside in addition to penicillin for effective therapy. However, other authors recommend the addition of an aminoglycoside to