Penicillin sensitive streptococcal endocarditis. In vitro and clinical observations on penicillin streptomycin therapy
The in vitro activity of penicillin and streptomycin against 48 strains of viridans streptococci isolated from patients with endocarditis was studied. All strains were inhibited by penicillin, up to 0.4 μg/ml, and streptomycin, up to 200 μg/ml. The combination of penicillin, 0.8 μg/ml, and streptomycin, 5 μg/ml, sterilized a 106 inoculum of 37 of the 48 strains. Penicillin, 1.6 μg/ml, killed only 1 strain, and none were killed by streptomycin, 10 μg/ml. Rate of killing was also increased for 45 of the 48 strains by the addition of streptomycin to penicillin. Over 100 patients with endocarditis caused by penicillin sensitive strains of viridans streptococci (minimal inhibitory concentration, ≤ 0.1 μg/ml) have been treated with parenteral penicillin and streptomycin for 2 wk followed by parenteral penicillin alone for an additional 2 wk, without relapse. Penicillin, in combination with streptomycin, appears to be the optimal therapy for viridans streptococcal endocarditis.