Silver Dressings – a Balance Between Antimicrobial Efficacy and Healing Promotion

Introduction: Silver within a dressing must be in its ionic state (Ag1+) for antimicrobial efficacy. However, to combat biofilm, additional components such as EDTA and benzethonium chloride (BC) may be required. Dressings containing Ag Oxyalts are unique in their ability to produce higher oxidative states of silver (Ag2+/Ag3+). These higher oxidative states of silver are potently antimicrobial. We compared the effectiveness of Ag Oxysalt dressings to Ag1+ or Ag1+ + EDTA/BC dressings against wound biofilms. We also examined if the potent nature of these antimicrobial dressings has an adverse effect on healing independent of infection. 

Methods: Dressings were applied to excisional mouse wounds infected with Pseudomonas aeruginosa or Staphylococcus aureus biofilms. Wounds were harvested after 3 and 7 days and the efficacy assessed using plate counts and florescent in situ hybridisation (FISH). Wound area and re-epithelialisation was quantified from histological analysis. The effects of the silver dressings on healing independent of infection was assessed from histological analysis of uninfected mouse wounds treated for 3 days. 

Results: Plate counts and FISH revealed Ag Oxysalt and Ag1+ + EDTA/BC dressings reduced viable bacteria in biofilm infected mouse wounds to a greater extent than Ag1+ dressings. However, biofilm infected wounds treated with Ag Oxysalt dressings were significantly smaller, with greater re-epithelialisation and significantly fewer neutrophils and macrophage compared control, Ag1+ and Ag1+ + EDTA/BC treatment. Finally, compared to control treatment, uninfected wounds treated with Ag Oxysalt dressings were significantly smaller with greater re-epithelialisation whereas Ag1+ + EDTA/BC treated wounds were larger with significantly less re-epithelialisation.

Conclusion: Potent antimicrobial dressings are required to effectively kill bacteria within a biofilm but the potent nature of these dressings can have detrimental effects on healing independent of infection. Ag Oxysalt dressings kill bacteria within a biofilm yet promote healing independent of infection.