In vitro susceptibility and molecular analysis of gentamicin-resistant enterococci

Enterococci with gentamicin MICs of 256 to 1,024 mu g/mL were evaluated for susceptibility to ampicillin pins gentamicin synergism. Sixteen of eightee n enterococcal isolates were not susceptible to synergistic killing by ampi cillin plus gentamicin; II possessed aac(6')-aph(2 "), and 4 possessed aph( 2 ")-Ic. A gentamicin MIC of 512 ou 1,024 mu g/mL predicted lack of ampicil lin/gentamicin synergism, but a gentamicin MIC of 256 mu g/mL did not. For six enterococcal strains possessing the gentamicin-resistance gene aph(2 ") -Ic, ampicillin pills dibekacin, ampicillin plus netilmicin, and ampicillin pills amikacin produced synergistic killing in five, three, and two strain s, respectively. (C) 1998 Elsevier Science Inc.