Is ampicillin plus cephalosporins a therapeutic option for Ampicillin-Susceptible Enterococcus faecium?

Enterococcus faecium, a significant hospital associated pathogen, poses substantial treatment challenges. While combinations of ampicillin with cephalosporins are first-line therapies to treat Enterococcus faecalis high-mortality-rates infections, their efficacy against ampicillin-susceptible E. faecium (ASEfm) is less clear. This study evaluates the effectiveness of combining ampicillin with ceftriaxone or ceftaroline against ASEfm strains. Ten ASEfm bloodstream isolates from complicated infections were analyzed. Susceptibility to several antibiotics, including ceftriaxone, ceftaroline, and cefotaxime, was determined using standard methods. Time-kill assays were conducted to assess the synergistic and additive effects of ampicillin in combination with ceftriaxone or ceftaroline. Time-kill studies revealed that ampicillin combined with ceftaroline demonstrated synergistic and/or additive effects in 7 out of 10 strains analyzed. In contrast, ampicillin combined with ceftriaxone showed less pronounced synergy, with only 3 out of 10 strains exhibiting synergistic and/or additive effects. Our findings indicate that ampicillin combined with ceftaroline, or ceftriaxone provides synergistic activity against some but not all ASEfm clinical isolates. The observed synergy suggests that these combinations could offer a potential therapeutic option for challenging ASEfm infections.