Standardizing an in vitro procedure for the evaluation of the antimicrobial activity of wound dressings and the assessment of three wound dressings

A wide selection of wound dressings is available on the market with varying claims of antimicrobial efficacy. A valid standard method for evaluation of their antimicrobial activity in vitro has not been established. In this study we suggest a standardized timekill assay procedure for antimicrobial activity evaluation of wound dressings in order to make studies more comparable and reproducible. We also tested two silver-containing dressings and one propolis-containing dressing against Staphylococcus aureus, Streptococcus pyogenes, Escherichia coli and Pseudomonas aeruginosa using our proposed procedure. The following dressings were tested: the ionic silver-containing dressing (ISCD), nanocrystalline silver coated dressing (NSCD) and a propolis-containing dressing (PCD) that is in development. A timekill assay and the zone of inhibition test were used in the study. NSCD exhibited the most potent antibacterial activity against all organisms. ISDC also demonstrated good antibacterial activity although inferior to NSCD. PCD did not show any bactericidal effect. Based on our findings we suggest that a timekill assay with a 1 cm(2) dressing is used for evaluation of the antimicrobial activity of wound dressings, and that the dressings should be exposed to a standardized inoculum of 11.510(6) cfu/mL with MuellerHinton broth as the most appropriate medium. PCD requires further research to establish its clinical value.