title: In vitro activity of retapamulin against linezolid and methicillin-resistant Staphylococcus aureus isolates.
abstract: OBJECTIVE
  To determine the in vitro activity of retapamulin and other topical antibiotics (mupirocin, bacitracin, and fusidic acid) usually employed for nasal decolonization, against methicillin-susceptible Staphylococcus aureus (MSSA), methicillin-resistant S. aureus (MRSA), and linezolid and methicillin-resistant S. aureus.
  
  
  METHODS
  The minimum inhibitory concentrations (MICs) were determined on Mueller-Hinton agar according to the guidelines of the Clinical and Laboratory Standards Institute and of the European Committee for Antimicrobial Susceptibility Testing. Presence of the cfr gene in linezolid and methicillin-resistant S. aureus isolates was detected using polymerase chain reaction.
  
  
  RESULTS
  Retapamulin inhibited all the isolates of MSSA and MRSA at 0.125 mg/L, but the 18 linezolid-resistant-MRSA strains proved resistant, with MICs over 32 mg/L. Most MSSA isolates (9/10) were susceptible to mupirocin with MICs under 0.19 mg/L, although this value decreased to half against MRSA, and almost all linezolid-resistant MRSA (17/18) strains were resistant to mupirocin with an MIC range of between 8 mg/L and 28 mg/L. The MIC of fusidic acid increased substantially against linezolid-resistant MRSA, whereas that of bacitracin showed no differences.
  
  
  CONCLUSIONS
  Retapamulin demonstrated excellent in vitro activity against MSSA and MRSA strains, but not against MRSA isolates harbouring the cfr gene. The results of this in vitro study support cut-off values for retapamulin of ≤ 0.5, 1, and ≥ 2 mg/L for susceptible, intermediate, and resistant strains, respectively.
authors.affiliation: Department of Clinical Microbiology and Infectious Diseases, Hospital Clinico San Carlos, Universidad Complutense, Madrid, Spain. fj.candel@terra.es
authors.forename: F J
authors.initials: FJ
authors.lastname: Candel
authors.forename: G
authors.initials: G
authors.lastname: Morales
authors.forename: J J
authors.initials: JJ
authors.lastname: Picazo
mesh_terms: D000081:Acetamides / Q000494:pharmacology*; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001414:Bacitracin / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology*; D004224:Diterpenes; D000069349:Linezolid; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics; D008826:Microbial Sensitivity Tests; D016712:Mupirocin / Q000494:pharmacology; D023303:Oxazolidinones / Q000494:pharmacology*; D016133:Polymerase Chain Reaction; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics
chemical_list: D000081:Acetamides; D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D019086:Bridged Bicyclo Compounds, Heterocyclic; C539943:CFR protein, Staphylococcus aureus; D004224:Diterpenes; D023303:Oxazolidinones; D001414:Bacitracin; C508887:retapamulin; D016712:Mupirocin; D000069349:Linezolid