Background: Silver-containing negative-pressure wound therapy (NPWT) foam dressings should reduce the microbial load of infected surgical sites and thereby promote healing. The effects of silver and an experimental copper coating of NPWT dressings on the growth kinetics of methicillin-resistant Staphylococcus aureus (MRSA) were investigated with a focus on the importance of the initial bacterial load and the incubation time.
Methods: Commercially available foam samples with and without silver coating were inoculated in vitro with six MRSA suspensions differing in bacterial concentration (1.85×10(3) to 1.85×10(8) colony-forming units per milliliter [CFU/mL]). In a second series, uncoated, silver-containing and experimental copper-coated foam samples were inoculated with one MRSA suspension (1.85×10(6) CFU/mL). The MRSA viable counts in the entrapped fluid were evaluated statistically after 1, 3, 7, and 14 d incubation.
Results: Silver foam samples reduced MRSA counts by two decimal powers compared with the corresponding inocula. With respect to the uncoated samples, silver coating reduced MRSA concentrations by up to 7 logs, which was significant (p≤0.045) for all groups except the one with the highest MRSA concentration. The antibacterial effect of copper became apparent only after 7 d, but thereafter was far more pronounced than the effects of silver (p<0.01 after 14 d).
Conclusions: Antimicrobial-coated foam dressings showed significant in vitro antibacterial properties and thus could be advantageous in the treatment of MRSA-infected incisions.