High-level gentamicin-resistant enterococci: in vitro activity of double and triple combinations of antimicrobial drugs.

The ability of double and triple combinations of antimicrobials with different mechanisms of action, such as teicoplanin, meropenem, gentamicin and sparfloxacin, to achieve synergisms was investigated in vitro on some moderate-level gentamicin-resistant (MLGR: 8 < or = MIC < or = 256 mg/l) and high-level gentamicin-resistant (HLGR: MIC > 500 mg/l) enterococci. On MLGR strains, a constant synergistic effect was achieved by a combination of teicoplanin with gentamicin or with meropenem, while generally addition, sometimes close to synergism, was exhibited by gentamicin-meropenem, gentamicin-sparfloxacin and teicoplanin-sparfloxacin associations. Triple combinations of teicoplanin, meropenem and gentamicin, or teicoplanin, sparfloxacin and gentamicin, always showed a remarkable advantage in terms of synergism over double combinations. On HLGR enterococci, the only double association showing an additive effect, sometimes close to synergism, was teicoplanin plus meropenem, while the triple combination of teicoplanin with gentamicin and meropenem always showed a marked synergistic effect. An effect very close to synergism was also shown by the combination of teicoplanin with sparfloxacin and gentamicin.