Potential factors contributing to the poor antimicrobial efficacy of SAAP-148 in a rat wound infection model

Ann Clin Microbiol Antimicrob. 2019 Dec 3;18(1):38. doi: 10.1186/s12941-019-0336-7.


Background: We investigated the efficacy of a synthetic antimicrobial peptide SAAP-148, which was shown to be effective against Methicillin-resistant Staphylococcus aureus (MRSA) on tape-stripped mice skin. Unexpectedly, SAAP-148 was not effective against MRSA in our pilot study using rats with excision wounds. Therefore, we investigated factors that might have contributed to the poor efficacy of SAAP-148. Subsequently, we optimised the protocol and assessed the efficacy of SAAP-148 in an adapted rat study.

Methods: We incubated 100 µL of SAAP-148 with 1 cm2 of a wound dressing for 1 h and determined the unabsorbed volume of peptide solution. Furthermore, 105 colony forming units (CFU)/mL MRSA were exposed to increasing dosages of SAAP-148 in 50% (v/v) human plasma, eschar- or skin extract or PBS. After 30 min incubation, the number of viable bacteria was determined. Next, ex vivo skin models were inoculated with MRSA for 1 h and exposed to SAAP-148. Finally, excision wounds on the back of rats were inoculated with 107 CFU MRSA overnight and treated with SAAP-148 for 4 h or 24 h. Subsequently, the number of viable bacteria was determined.

Results: Contrary to Cuticell, Parafilm and Tegaderm film, < 20% of peptide solution was recovered after incubation with gauze, Mepilex border and Opsite Post-op. Furthermore, in plasma, eschar- or skin extract > 20-fold higher dosages of SAAP-148 were required to achieve a 2-log reduction (LR) of MRSA versus SAAP-148 in PBS. Exposure of ex vivo models to SAAP-148 for 24 h resulted in a 4-fold lower LR than a 1 h or 4 h exposure period. Additionally, SAAP-148 caused a 1.3-fold lower mean LR at a load of 107 CFU compared to 105 CFU MRSA. Moreover, exposure of ex vivo excision wound models to SAAP-148 resulted in a 1.5-fold lower LR than for tape-stripped skin. Finally, SAAP-148 failed to reduce the bacterial counts in an adapted rat study.

Conclusions: Several factors, such as absorption of SAAP-148 by wound dressings, components within wound exudates, re-colonisation during the exposure of SAAP-148, and a high bacterial load may contribute to the poor antimicrobial effect of SAAP-148 against MRSA in the rat model.

Keywords: Antimicrobial peptides; Efficacy; Methicillin-resistant Staphylococcus aureus; SAAP-148; Skin and soft tissue infections; Topical therapy.

MeSH terms

  • Administration, Topical
  • Animals
  • Anti-Bacterial Agents / administration & dosage
  • Anti-Bacterial Agents / pharmacology
  • Methicillin-Resistant Staphylococcus aureus / drug effects
  • Pilot Projects
  • Rats
  • Skin / microbiology
  • Staphylococcal Infections / drug therapy*
  • Staphylococcal Infections / microbiology
  • Staphylococcus aureus / drug effects*
  • Synthetic Drugs / administration & dosage
  • Synthetic Drugs / pharmacology*
  • Wound Infection* / drug therapy
  • Wound Infection* / microbiology


  • Anti-Bacterial Agents
  • Synthetic Drugs