title: Activity of daptomycin or linezolid in combination with rifampin or gentamicin against biofilm-forming Enterococcus faecalis or E. faecium in an in vitro pharmacodynamic model using simulated endocardial vegetations and an in vivo survival assay using Galleria mellonella larvae.
abstract: Enterococci are the third most frequent cause of infective endocarditis. A high-inoculum stationary-phase in vitro pharmacodynamic model with simulated endocardial vegetations was used to simulate the human pharmacokinetics of daptomycin at 6 or 10 mg/kg of body weight/day or linezolid at 600 mg every 12 h (q12h), alone or in combination with gentamicin at 1.3 mg/kg q12h or rifampin at 300 mg q8h or 900 mg q24h. Biofilm-forming, vancomycin-susceptible Enterococcus faecalis and vancomycin-resistant Enterococcus faecium (vancomycin-resistant enterococcus [VRE]) strains were tested. At 24, 48, and 72 h, all daptomycin-containing regimens demonstrated significantly more activity (decline in CFU/g) than any linezolid-containing regimen against biofilm-forming E. faecalis. The addition of gentamicin to daptomycin (at 6 or 10 mg/kg) in the first 24 h significantly improved bactericidal activity. In contrast, the addition of rifampin delayed the bactericidal activity of daptomycin against E. faecalis, and the addition of rifampin antagonized the activities of all regimens against VRE at 24 h. Also, against VRE, the addition of gentamicin to linezolid at 72 h improved activity and was bactericidal. Rifampin significantly antagonized the activity of linezolid against VRE at 72 h. In in vivo Galleria mellonella survival assays, linezolid and daptomycin improved survival. Daptomycin at 10 mg/kg improved survival significantly over that with linezolid against E. faecalis. The addition of gentamicin improved the efficacy of daptomycin against E. faecalis and those of linezolid and daptomycin against VRE. We conclude that in enterococcal infection models, daptomycin has more activity than linezolid alone. Against biofilm-forming E. faecalis, the addition of gentamicin in the first 24 h causes the most rapid decline in CFU/g. Of interest, the addition of rifampin decreased the activity of daptomycin against both E. faecalis and VRE.
authors.affiliation: Department of Pharmacy Practice, University of Rhode Island, Kingston, Rhode Island, USA Rhode Island Infectious Diseases (RIID) Research Program Laboratory, Providence Veterans Affairs Medical Center, Providence, Rhode Island, USA.
authors.forename: Megan K
authors.initials: MK
authors.lastname: Luther
authors.affiliation: Division of Infectious Diseases, Warren Alpert Medical School of Brown University, Providence, Rhode Island, USA Rhode Island Hospital, Providence, Rhode Island, USA.
authors.forename: Marios
authors.initials: M
authors.lastname: Arvanitis
authors.affiliation: Division of Infectious Diseases, Warren Alpert Medical School of Brown University, Providence, Rhode Island, USA Rhode Island Hospital, Providence, Rhode Island, USA.
authors.forename: Eleftherios
authors.initials: E
authors.lastname: Mylonakis
authors.affiliation: Department of Pharmacy Practice, University of Rhode Island, Kingston, Rhode Island, USA Rhode Island Infectious Diseases (RIID) Research Program Laboratory, Providence Veterans Affairs Medical Center, Providence, Rhode Island, USA Division of Infectious Diseases, Warren Alpert Medical School of Brown University, Providence, Rhode Island, USA KerryLaPlante@uri.edu.
authors.forename: Kerry L
authors.initials: KL
authors.lastname: LaPlante
mesh_terms: D000081:Acetamides / Q000493:pharmacokinetics* / Q000494:pharmacology; D000818:Animals; D000900:Anti-Bacterial Agents / Q000493:pharmacokinetics / Q000494:pharmacology; D018441:Biofilms / Q000187:drug effects* / Q000254:growth & development; D015169:Colony Count, Microbial; D017576:Daptomycin / Q000493:pharmacokinetics* / Q000494:pharmacology; D004347:Drug Interactions; D004359:Drug Therapy, Combination; D013293:Enterococcus faecalis / Q000187:drug effects* / Q000502:physiology; D016984:Enterococcus faecium / Q000187:drug effects* / Q000502:physiology; D005839:Gentamicins / Q000493:pharmacokinetics* / Q000494:pharmacology; D006801:Humans; D007814:Larva / Q000187:drug effects / Q000382:microbiology; D000069349:Linezolid; D008826:Microbial Sensitivity Tests; D008954:Models, Biological; D015233:Models, Statistical; D009036:Moths / Q000187:drug effects / Q000382:microbiology; D023303:Oxazolidinones / Q000493:pharmacokinetics* / Q000494:pharmacology; D012293:Rifampin / Q000493:pharmacokinetics* / Q000494:pharmacology
chemical_list: D000081:Acetamides; D000900:Anti-Bacterial Agents; D005839:Gentamicins; D023303:Oxazolidinones; D000069349:Linezolid; D017576:Daptomycin; D012293:Rifampin