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In Vitro Activity of Retapamulin against Staphylococcus aureus Resistant to Various Antimicrobial Agents

Louis D Saravolatz1, Joan Pawlak2, Stephanie N Saravolatz2

  • 1St. John Hospital and Medical Center and Wayne State University School of Medicine, Detroit, Michigan, USA louis.saravolatz@stjohn.org.

Antimicrobial Agents and Chemotherapy
|June 26, 2013
PubMed

Insights

Retapamulin shows strong activity against methicillin-resistant Staphylococcus aureus (MRSA), including strains resistant to other antibiotics. It remains effective against most mupirocin-resistant MRSA, offering a potential treatment option.

Area of Science:

  • Microbiology
  • Infectious Diseases
  • Antimicrobial Resistance

Background:

  • Methicillin-resistant Staphylococcus aureus (MRSA) poses a significant threat due to rising antimicrobial resistance.
  • Existing treatments are becoming less effective against multidrug-resistant MRSA strains, including those resistant to vancomycin, linezolid, daptomycin, and mupirocin.

Purpose of the Study:

  • To evaluate the in vitro activity of retapamulin against a panel of clinical MRSA isolates.
  • To assess retapamulin's efficacy against MRSA strains exhibiting resistance to key antibiotics, including vancomycin, linezolid, daptomycin, and mupirocin.
  • To compare retapamulin's activity with mupirocin against susceptible and resistant MRSA isolates.

Main Methods:

  • Microdilution tests were employed to determine the minimum inhibitory concentrations (MICs) of retapamulin and six other antimicrobial agents against 155 MRSA isolates.
  • Time-kill assays were conducted on representative MRSA, vancomycin-intermediate S. aureus (VISA), and vancomycin-resistant S. aureus (VRSA) isolates.
  • Isolates included strains with documented resistance to vancomycin, linezolid, daptomycin, and mupirocin.

Main Results:

  • Retapamulin demonstrated potent activity with a MIC90 of 0.12 μg/ml against the tested MRSA isolates.
  • Mupirocin showed a higher MIC90 of 8 μg/ml, with 10% of isolates exhibiting resistance.
  • Retapamulin maintained excellent activity against 94% (15/16) of mupirocin-resistant MRSA isolates.

Conclusions:

  • Retapamulin exhibits significant in vitro activity against a broad range of MRSA isolates, including those with resistance to vancomycin, linezolid, and daptomycin.
  • Retapamulin is effective against the majority of mupirocin-resistant MRSA strains, suggesting its potential utility in treating infections caused by these challenging pathogens.
  • These findings support retapamulin as a valuable therapeutic option for MRSA infections, particularly where resistance to other agents is a concern.

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