title: In vitro effect of the presence of human albumin or human serum on the bactericidal activity of daptomycin against strains with the main resistance phenotypes in Gram-positives.
abstract: OBJECTIVE
  Bactericidal activity depends on antibiotic-bacteria couples, resistance phenotype and theoretically on protein binding. This work explores the influence of protein binding on the bactericidal activity of two antibiotics, daptomycin versus vancomycin, that exhibit, respectively, different C(max) (56 versus 25.5 mg/L), protein binding (91.7% versus 36.9%) and thus theoretical free-drug fractions (4.7 versus 16.1 mg/L).
  
  
  METHODS
  The effect of the presence of physiological concentrations of human albumin (4 g/dL) or human serum (90%) on the bactericidal activity of daptomycin was studied against Gram-positive isolates with troublesome resistance phenotypes [multidrug-resistant Streptococcus pneumoniae (MDRSP), methicillin-resistant Staphylococcus aureus (MRSA), heterogeneous vancomycin-intermediate MRSA (MRSA-hVI) and vancomycin-resistant Enterococcus faecium]. Killing curves (final inocula of approximately 10(7) cfu/mL) were performed using daptomycin and vancomycin concentrations similar to the C(max) obtained in serum.
  
  
  RESULTS
  Daptomycin was rapidly bactericidal (> or =3 log(10) initial inocula reduction) against S. pneumoniae and S. aureus, regardless of the strain tested or the presence of albumin or human serum (that slightly delayed bactericidal activity). Against vancomycin-susceptible or -resistant enterococci, daptomycin exhibited rapid bactericidal activity, delayed to 8 and 24 h, respectively, by human albumin. Vancomycin exhibited much slower bactericidal activity against MDRSP and methicillin-susceptible or -resistant S. aureus, but was never bactericidal against MRSA-hVI and vancomycin-susceptible or -resistant E. faecium.
  
  
  CONCLUSIONS
  Daptomycin exhibited rapid bactericidal activity against the strains of the three Gram-positive species tested, regardless of resistance phenotype or the presence of physiological concentrations of albumin.
authors.affiliation: Microbiology Department, School of Medicine, Universidad Complutense, Avda Complutense s/n, Madrid, Spain.
authors.forename: F
authors.initials: F
authors.lastname: Cafini
authors.forename: L
authors.initials: L
authors.lastname: Aguilar
authors.forename: N
authors.initials: N
authors.lastname: González
authors.forename: M J
authors.initials: MJ
authors.lastname: Giménez
authors.forename: M
authors.initials: M
authors.lastname: Torrico
authors.forename: L
authors.initials: L
authors.lastname: Alou
authors.forename: D
authors.initials: D
authors.lastname: Sevillano
authors.forename: P
authors.initials: P
authors.lastname: Vallejo
authors.forename: J
authors.initials: J
authors.lastname: Prieto
mesh_terms: D000668:Ampicillin Resistance; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D015169:Colony Count, Microbial; D017576:Daptomycin / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial / Q000187:drug effects*; D016984:Enterococcus faecium / Q000187:drug effects; D006094:Gram-Positive Bacteria / Q000187:drug effects*; D006801:Humans; D008826:Microbial Sensitivity Tests; D010641:Phenotype; D044967:Serum; D012709:Serum Albumin / Q000494:pharmacology*; D013211:Staphylococcus aureus / Q000187:drug effects; D013296:Streptococcus pneumoniae / Q000187:drug effects; D014640:Vancomycin / Q000494:pharmacology; D020713:Vancomycin Resistance
chemical_list: D000900:Anti-Bacterial Agents; D012709:Serum Albumin; D014640:Vancomycin; D017576:Daptomycin