Evaluation of Antibacterial Properties of Light-Exposed, Discolored, Postoperative Silver Foam Dressing

Light exposure can cause the discoloration of silver dressings. Due to sterilization requirements, all silicone dressings with or without silver are packaged in non-foil materials. These materials are not impermeable to light, so a certain amount of discoloration is always possible due to light exposure in the manufacturing processor or when taken out of its carton. The purpose of the study was to assess the antibacterial efficacy of a postoperative silver foam dressing that was discolored due to light exposure.

The test silver dressing was compared to a control, non-silver dressing. Samples were prepared into 1x1 inch sections and aseptically placed into sterile containers until the initial inoculations. The initial inoculum volume was 0.25 ml with 2.01x107 colony forming units (CFU)/ml for methicillin resistant Staphylococcus aureus and 2.01x107 CFU/ml for Serratia marcescens. The samples were assessed at t=0, 24 hours, 7 day,s and 14 days. For t=0, the samples were immediately neutralized and enumerated to obtain the initial recovery of each sample types. The samples for t=24 hours, 7 days, and 14 days were placed into 30–35◦C/70% RH chamber until the designated exposure times. For t=7 days, repeat inoculations were done at days 1 and 4, and for t=14 days, repeat inoculations were done at days 4, 8, and 11. Testing was performed in triplicate for each time point, and the averages of the replicated were used for log10 reduction calculations.

At t=24 hours, 7 days, and 14 days, the postoperative silver foam dressings showed a >4 log reduction against MRSA and S. marcescens.

This study demonstrates that the discolored, postoperative silver foam dressing has potent antimicrobial action against MRSA and S. marcescens for up to 14 days in vitro. The clinical implications of these findings have yet to be determined.