Bactericidal activities of peptide antibiotics against multidrug-resistant Enterococcus faecium

Multidrug-resistant Enterococcus faecium has emerged as a serious pathogen for which no effective therapy has been established. In this report, we describe the activities of two peptide antibiotics, ramoplanin and daptomycin, against 15 isolates of E. faecium resistant to vancomycin, ampicillin, and aminoglycosides using time-kill experiments. Both antibiotics were rapidly bactericidal when tested in broth; however, the addition of 50% serum resulted in significant regrowth. The combination of ampicillin with either ramoplanin or daptomycin largely prevented this regrowth. These peptide antibiotics showed good activity against these pathogens. While the development of daptomycin has been halted, ramoplanin may hold promise for the therapy of multidrug-resistant E. faecium, especially when combined with ampicillin.