Synergistic activity of vancomycin and teicoplanin alone and in combination with streptomycin against Enterococcus faecalis strains with various vancomycin susceptibilities

The synergy between two glycopeptides, vancomycin (Vm) and teicoplanin (Tec) and streptomycin (Sm) was studied by time-kill method. Five clinical vanB resistant Enterococcus faecalis (ENC) isolates with variable Vm-susceptibility were used. Different concentrations of Vm, Tec and Sm representing therapeutic concentrations were combined. Antibacterial activity was related to the concentrations of Vm and Sm, and Vm susceptibility to ENC. For strains with Vm MIC up to 64 mg/l, synergy was achieved with higher concentrations of Vm and Sm, while all combinations of Tec and Sm were synergistic against all strains except ENC 29. For ENC 29 with Vm MIC of 512 mg/l and Tec MIC of <1 mg/l, none of the combinations was synergistic. The significance of these in vitro results needs further investigation in vivo.