title: The bactericidal activity of ampicillin, daptomycin, and vancomycin against ampicillin-resistant Enterococcus faecium.
abstract: Ampicillin, daptomycin, and vancomycin, alone and in combination with gentamicin, were examined for bactericidal effects on ampicillin-resistant Enterococcus faecium using broth dilution minimum inhibitory concentrations (MICs) and time-kill studies. We tested 12 ampicillin-resistant isolates and demonstrated the following MICs and MBCs, respectively: ampicillin, greater than or equal to 32 micrograms/ml and greater than 256 micrograms/ml; daptomycin, less than or equal to 4 micrograms/ml and less than or equal to 16 micrograms/ml; and vancomycin, less than or equal to 4 micrograms/ml and greater than 64 micrograms/ml. Time-kill studies demonstrated that daptomycin alone had marked activity against the ampicillin-resistant E. faecium and that the addition of gentamicin resulted in synergistic killing. In addition, ampicillin and vancomycin were not bactericidal for the ampicillin-resistant isolates without the addition of gentamicin. The present study supports the consideration of daptomycin alone or in combination with an aminoglycoside as an alternative therapy for ampicillin-resistant enterococci, although additional clinical experience is now necessary.
authors.affiliation: Department of Laboratories, St. Christopher's Hospital for Children, Philadelphia, PA 19134-1095.
authors.forename: A
authors.initials: A
authors.lastname: el-Mady
authors.forename: J E
authors.initials: JE
authors.lastname: Mortensen
mesh_terms: D000667:Ampicillin / Q000494:pharmacology; D000668:Ampicillin Resistance; D017576:Daptomycin; D004347:Drug Interactions; D005839:Gentamicins / Q000494:pharmacology*; D006801:Humans; D008826:Microbial Sensitivity Tests; D010455:Peptides / Q000494:pharmacology; D013291:Streptococcus / Q000187:drug effects*; D014640:Vancomycin / Q000494:pharmacology*
chemical_list: D005839:Gentamicins; D010455:Peptides; D014640:Vancomycin; D000667:Ampicillin; D017576:Daptomycin