IN-VITRO EVALUATION OF HIGH-LEVEL, GENTAMICIN-RESISTANT ENTEROCOCCI ISOLATED FROM BACTEREMIC PATIENTS

We attempted to characterize the susceptibility of high-level, gentami cin-resistant: (HLGR, minimum inhibitory concentration [MIC] >2000 mu g/ml) enterococcal blood isolates and evaluated a small subset of thes e isolates for bactericidal synergy. Thirteen Enterococcus faecalis an d three Enterococcus faecium isolates that were HLGR were prospectivel y collected. Standard broth macrodilution techniques were used to dete rmine the MICs and minimum bactericidal concentrations to a variety of antibiotics. Two isolates were evaluated for synergy by time-kill cur ve methods using combinations of penicillin and streptomycin, teicopla nin and rifampin, and vancomycin and ciprofloxacin. Teicoplanin was th e most active antibiotic tested, with all isolates exhibiting suscepti bility to this agent. Four E. faecalis isolates and one E. faecium iso late expressed only low-level resistance to streptomycin (LLSR, MICs 3 2-64 mu g/ml). Penicillin and streptomycin produced bactericidal syner gy in the LLSR isolate. The other antibiotic combinations did not resu lt in bactericidal synergy in the two isolates tested. For HLGR entero cocci that are only LLSR, the combination of penicillin-streptomycin a ppears to provide adequate bactericidal activity Teicoplanin may poten tially be useful for streptomycin-resistant HLGR isolates.