Enterococci and aminoglycosides: evaluation of susceptibility and synergism of their combination with piperacillin.

Some clinical isolates of enterococci were tested for susceptibility to gentamicin, tobramycin, amikacin and netilmicin. Five percent of Streptococcus faecalis tested demonstrated high level resistance (minimum inhibitory concentration (MIC) greater than 2024 micrograms/ml) to gentamicin, tobramycin and netilmicin, while amikacin had MICs greater than 128 micrograms/ml for all strains tested. Since a combination of a beta-lactam and streptomycin does not produce synergism against all strains of enterococci for an increase in the number of highly resistant strains, the effect of piperacillin plus gentamicin, tobramycin, and netilmicin was examined. The combination piperacillin + netilmicin seemed to be very effective against all enterococci tested.