Enterococcus faecium resistant to ampicillin and gentamicin.

Thirty ampicillin-resistant enterococci were isolated from clinical specimens at our institution, 28 of these over a six month period. All were identified as Enterococcus faecium with an MIC(90) to ampicillin ond penicillin of 32 and 128 mug/ml, respectively. These isolates were also resistant to imipenem, ampicillin-sulbactam, and amoxicillin-clavulanic acid, but susceptible to vancomycin. Only 10%% were resistant to gentamicin at 2 000 mug/ml, but bactericidad synergy could not be demonstrated against any of these isolates using the combination of gentamicin added to either penicillin or vancomycin. No beta-lactamase activity was detected by the nitrocephin test, or by the addition of clavulanic acid or sulbactam. Plasmid analysis revealed a band common to 29 of 30 ampicillin-resistant E. faecium, which was not present in two ampicillin-sensitive E. faecium or in any of twenty E. faecalis. The limited number of options available to treat these isolates of E. faecium simultaneously resistant to multiple antibiotics and resistant to the bactericidad synergy of gentamicin underscores the need to develop new strategies in the prevention and treatment of enterococcal infections.