Treatment with
silver-containing
wound dressings is becoming an increasingly popular strategy to eliminate growth of opportunistic
wound pathogens during the healing process. However, there are concerns over the possible side-effects of
silver to the patient; coupled to the cost of
silver as an ingredient there is a desire to ensure that
wound dressings contain the least quantity of active ingredient to ensure the minimum bactericidal concentration (MBC) of
silver is maintained in the
wound environment. This requires the ability to determine the efficacy of
silver directly within the
wound environment; an extremely complicated task that is difficult using classical (plate counting) microbiological assays because these cannot be conducted in situ. Here, we report a quantitative method for determining the efficacy of
silver in
wound dressings using an isothermal calorimetric method. The growth curves of P. aeruginosa (NCIMB 8628) were recorded in growth medium and in growth medium containing
AQUACEL Ag Hydrofiber dressing. It was found that 10 mg of dressing was sufficient to ensure no detectable growth of organism in 2.5 mL of medium inoculated to 10(6) cfu/mL. This corresponded to a
silver load of 1.1x10(-6) moles (equivalent to 4.4x10(-4) M, in the volume of medium used in the experiment). Experiments conducted with
silver nitrate rather than dressing indicated the MBC of
silver against P. aeruginosa was 1x10(-4) M. The results suggested that not all of the
silver in the dressing was bioavailable, at least over the lifetime of the experiment. One advantage of this effect would be the lack of excess availability of the
silver, which allays fears of potential toxicity to the patient and may provide an extended period of time over which the dressing is bactericidal.