The antimicrobial activity of silver-containing dressings against surface-associated microorganisms in a dual-species community

Introduction: It is commonly accepted that bacteria found within hard-to-heal wounds exist as surface-associated or aggregated communities, often comprising multiple species.1,2 This polymicrobial nature increases virulence and tolerance to antimicrobial agents.3,4 We evaluated antimicrobial dressings containing silver against surfaced-associated microorganisms in a dual-species community grown in a stringent simulated wound model.Methods:Four silver-containing dressings were assessed: carboxymethylcellulose dressing containing ionic silver, ethylenediaminetetraacetic acid (EDTA) and benzethonium chloride (BEC; ‘CISEB’*); non-adherent polyethylene mesh with polyester core dressing containing silver oxysalts (‘PPSO’†); cellulose ethyl sulphonate fiber dressing containing ionic silver (‘CESIS’‡); and polyacrylate (polyabsorbent) fiber dressing with acrylic core containing silver sulphate (‘PSS’).  In brief, challenge microorganisms (Klebsiella pneumoniae and methicillin-resistant Staphylococcus aureus [MRSA]) were grown together on gauze to simulate the surface-associated phenotype and transferred to a simulated wound assembly (SWA). Test dressings were applied and covered with a transparent film dressing, and the SWA was then incubated at 35±3 ºC for up to 72 hours. Enumeration of surviving bacteria was performed in triplicate for each test dressing. A two-sample t-test was used to compare dressings.Results: CISEB resulted in significantly greater reduction in biofilm than PPSO and PSS at 24 and 48 hours (p