Endocarditis due to streptomycin-susceptible Enterococcus faecalis with high-level gentamicin resistance

A case of community-acquired endocarditis caused by Enterococcus (Streptococcus) faecalis with high-level resistance to gentamicin sulfate but not to streptomycin sulfate is described. Killing curves performed using achievable serum levels showed synergistic killing when streptomycin but not gentamicin, tobramycin, or amikacin was combined with penicillin G sodium or vancomycin hydrochloride. Combination therapy with vancomycin and streptomycin resulted in cure. Serum bactericidal levels indicated activity of the synergistic, as well as a nonsynergistic (vancomycin plus gentamicin), combination. Routine screening of blood isolates for high-level resistance to streptomycin and gentamicin can provide guidance for selection of therapeutic combinations in serious enterococcal infections, including endocarditis.