Bactericidal activity of five combinations of penicillin G with aminoglycosides against Streptococcus faecium.

Combinations of penicillin G and five aminoglycosides were tested against 7 strains of S. faecium. For all the strains that had a low-level of resistance to streptomycin, the combination of penicillin G with streptomycin was synergistic. Penicillin combined with either kanamycin or netilmicin was ineffective against all strains. The combination of penicillin and amikacin was synergistic against only one of the aminoglycoside-susceptible strains and ineffective against all the other strains. Penicillin G with gentamicin was the only combination synergistic against all strains. The clinical implications of these findings for the treatment of bacterial endocarditis caused by S. faecium are discussed.