Synergistic treatment of enterococcal endocarditis: in vitro and in vivo studies.

Combinations of penicillin G sodium or ampicillin plus streptomycin sulfate do not produce synergism against all strains of enterococci. This lack of synergism was considered the cause of the failure in the treatment of enterococcal endocarditis. The effect of various combinations of antibiotics on 15 enterococcus strains, which had been isolated from patients with enterococcal endocarditis, was examined. The antibiotics included those that interfere with cell-wall synthesis and those that act on cell metabolism. The in vitro results have shown that while penicillin- or ampicillin-streptomycin combination was not synergistic in eight of 15 strains, penicillin- or ampicillin-gentamicin sulfate combination was synergistic in 100% of the cases. We report seven cases of enterococcal endocarditis that were successfully treated with penicillin- or ampicillin-gentamicin combination, thus confirming the effectiveness of this therapeutic regimen.