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

Objectives: 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.

Methods: 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.

Results: 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.

Conclusions: 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.