There has been a recent surge in the use of
silver as an
antimicrobial agent in a wide range of domestic and clinical products, intended to prevent or treat
bacterial infections and reduce bacterial colonization of surfaces. It has been reported that the antibacterial and cytotoxic properties of
silver are affected by the assay conditions, particularly the type of growth media used in vitro. The toxicity of Ag+ to bacterial cells is comparable to that of human cells. We demonstrate that biologically relevant compounds such as
glutathione,
cysteine and human blood components significantly reduce the toxicity of
silver ions to clinically relevant pathogenic bacteria and primary human dermal fibroblasts (skin cells). Bacteria are able to grow normally in the presence of
silver nitrate at >20-fold the minimum inhibitory concentration (MIC) if Ag+ and
thiols are added in a 1:1 ratio because the reaction of Ag+ with extracellular
thiols prevents
silver ions from interacting with cells. Extracellular
thiols and human serum also significantly reduce the antimicrobial activity of
silver wound dressings
Aquacel-Ag (Convatec) and
Acticoat (Smith & Nephew) to Staphylococcus aureus, Pseudomonas aeruginosa and Escherichia coli in vitro. These results have important implications for the deployment of
silver as an
antimicrobial agent in environments exposed to
biological tissue or secretions. Significant amounts of money and effort have been directed at the development of
silver-coated medical devices (e.g. dressings,
catheters, implants). We believe our findings are essential for the effective design and testing of antimicrobial
silver coatings.