In vitro diffusion bed, 3-day repeat challenge 'capacity' test for antimicrobial wound dressings

The aim of this study was to develop an in vitro wound infection model that allows the comparison of the bacterial kill rate of antimicrobial wound dressings over the course of 3 days, with renewed microbial challenges each day, under realistic wound-like conditions. A test bed model of a moderately exuding wound was constructed from a hydrogel containing releasable foetal calf serum (FCS), and cellulose discs dosed with test microbes (Methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa) suspended in 50% FCS applied at the interface between the test dressing and the hydrogel test bed. Freshly prepared discs were used to challenge the same dressing over a 23-hour period for a course of 3 days. Different test dressings produced differing kill rates, allowing quantitative comparison of both their immediate activity and their capacity to continue working over 3 days, within a fluid-donating system similar to the situation in vivo. The reported method has significant advantages over established test procedures since it enables the researcher to assess the antimicrobial capacity of wound dressings to continue working under conditions that match those encountered in wounds. These key conditions are those that would be expected to impede the action of the dressing and protect the infecting organisms.