Prosthetic-Valve Endocarditis Caused by Penicillin-ResistantStreptococcus mitis

To the Editor: Penicillin resistance has been an increasing problem in the treatment of infections due to gram-positive cocci over the past 15 years.1 Much of the concern has related to the rising minimal inhibitory concentrations (MICs) of antibiotics required to suppress Streptococcus pneumoniae, but sharp declines in penicillin sensitivity have also been observed in streptococci of the viridans group and S. mitis in particular.2–4 I report a case of prosthetic-valve endocarditis resulting from infection with an S. mitis organism that was fully resistant to penicillin. The patient, a 48-year-old man with a long history of intravenous drug abuse . . .