For serous enterococcal infections, synergistic combination of penicillin and aminoglycosides is recommended for bactericidal therapy. However, an optimal synergistic combination for infection caused by enterococcal strains demonstrating a high
level
resistance to aminoglycosides has not been established. The present study examined the in vitro effects of combinations of penicillin plus trimethoprim/sulfamethoxazole(Sxt), ciprofloxacin, teicoplanin, vancomycin, and fosfomycin and compared
with
single drug therapy of ampicillin of low(5㎍/mL) and high doses(10, 20㎍/mL) in strains of Enterococcus with high-level resistance to gentamicin, amikacin, and streptomycin by time kill studies. The minimal bactericidal concentrations of these
antibiotics were also determined. Sxt and ampicillin were most active single agents on both MIC/MBC test and time kill study, but not consistently bactericidal Only penicillin-ciprofloxacin combination exhibited significant bactericidal synergy
but
the
bactericidal effect was strain and inoculum-size dependent and not more significantly effective than high-dose ampicillin or Sxt only.
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