A previously described model of experimental Streptococcus faecalis
endocarditis in rabbits without an
indwelling catheter during the infectious processes was used to study the effect of long-term treatment with
antibiotics. Groups of animals infected with six different strains were treated for four weeks and the following parameters were determined: survival rate, bacterial concentration in blood and vegetations, signs at autopsy indicating
congestive heart failure. Before the therapeutic experiments, the tolerance of the rabbit to long-term exposure of the drugs
penicillin and
streptomycin was considered in a group of non-infected animals. Two out of 20 rabbits died with
enteritis during the
penicillin exposure, and a general
weight reduction was observed.
Streptomycin was apparently completely harmless. There was no
therapeutic effect of
streptomycin on S. faecalis
endocarditis due to strains all designated resistant to
streptomycin by MIC, except in rabbits infected with a strain, which showed partial susceptibility to the
drug by IC50. Regardless of the
therapeutic effect, evidence was obtained for rapid development of increased resistance of the infecting strains towards
streptomycin. After long-term treatment with
penicillin in either low or high dose some of the animals survived and the valves were sterilized in 37% of the animals after low-dose and in 39% after high-dose. It was observed that
congestive heart failure occurred with the greatest frequency and intensity after
infection with proteolytic strains.