The anti-microbial potential of silver has long been recognised, with many applications appearing in recent years with efficacy based on silver activity. However, concerns about silver toxicity often limits their use to topical applications with the antimicrobial efficacy balanced against the risk of silver-ions leaching out into tissue.

Chitosan (polyD-glucosamine) has been claimed to have anti-microbial and wound-healing properties that when combined with ionic silver have been used on, for example, burn victims. In this trial, the anti-microbial efficacy of Chitosan, bound with atomic silver, was evaluated against a range of cutaneous fungal and bacterial pathogens, including Trichophyton equinum, Malassezia pachydermatis, Dermatophilus congolensis and Staphylococcus aureus (including MRSA). Efficacy was tested using a spread plate method onto which blank antibiotic discs, coated with the either chitosan-Ag cream (Ag at 0.25%) or Chitosan-Ag powder (Ag at 4%), were applied. Plates with SDA and BBA were inoculated with 100µl of T.equinum or M.pachydermatis; and 100ul of D.congolensis or MRSA, respectively. Two control discs (sterile water and cream base) and two test discs (chitosan-Ag cream and chitosan-Ag powder) were applied to the plate and subsequently incubated until adequate growth occurred. Inhibition was then observed, comparing test versus control discs.

No apparent difference in inhibition of T.equinum was observed by controls and Chitosan-Ag cream but contact inhibition was observed by Chitosan-Ag powder. No apparent difference in inhibition of M.pachydermatis was observed by controls and Chitosan-Ag cream but clear inhibition was observed by Chitosan-Ag powder. No apparent difference in inhibition of D.congolensis was observed between controls but clear inhibition was observed by both Chitosan-Ag cream and Chitosan-Ag powder. No apparent difference in inhibition of MRSA was observed between controls but clear inhibition was observed by both Chitosan-Ag cream and Chitosan-Ag powder.

Results indicated that the tested fungal pathogens were more resistant and required a higher Chitosan-Ag concentration to be inhibited. Results further demonstrated the inhibition by Chitosan-Ag cream or powder of common cutaneous bacterial pathogens. Specifically the inhibition of D.congolensis and MRSA offers the prospect of using Chitosan-Ag as an antimicrobial barrier-cream/powder for mud fever, superficial cuts or post-surgical wounds.