Chemotherapy of experimental streptococcal endocarditis. II. Synergism between penicillin and streptomycin against penicillin-sensitive streptococci.

Bacterial endocarditis was produced by intravenous injection of Streptococcus viridans into rabbits with preexisting sterile endocardial vegetations. After 6 h had elapsed, bacteria in the vegetations could not be eradicated by brief treatment with antimicrobials to which the streptococci were sensitive. However, when treatment with penicillin was continued for 4 days, the animals were cured. The 6-h infection therefore offered a model in which treatments could be conveniently compared over a short period. Synergism was demonstrated between penicillin and streptomycin in endocarditis due to a fully penicillin-sensitive streptococcus, a point which had not been previously proved in vivo. The clinical implications are discussed.