Penicillin-resistant Streptococcus constellatus as a cause of endocarditis.

Endocarditis in a 2-year-old child was caused by a penicillin-resistant Streptococcus constellatus. Viridans streptococci in general and those associated with endocarditis in particular are usually believed to be penicillin sensitive. Although the patient did not receive prophylactic antibiotics, the child had recently been treated with an oral penicillin. Penicillin-resistant viridans streptococci are usually sensitive to the synergistic effects of penicillin and an aminoglycoside, but this organism was not. Clindamycin was ultimately shown to demonstrate admirable bactericidal activity against this patient's S constellatus.