Antimicrobial Activity of Electrochemical Silver Ions in Nonionic Surfactant Solutions and in Model Dispersions

Abstract

The microbicidal effectiveness against Gram-positive and Gram-negative bacteria and Candida albicans of electrochemical silver ions in aqueous solutions containing nonionic surfactants was investigated. From the perspective of the possible use of anodic silver as a preservative in cosmetic or pharmaceutical preparations, microbicidal efficacy was also studied in oil/water model dispersions. Surfactants and botanical extracts partially inhibited the microbicidal effectiveness of anodic silver. Nevertheless in all the experimental conditions, silver ions reduced the microbial concentration up to 4 log units of the starting inoculum in less than 6 h. The wide microbicidal spectrum and the high rate of kill of silver ions appear, therefore, attractive enough to suggest a possible utilization of anodic silver as a preserving agent.

Utilization of electrochemical silver ions as preservative agent in cosmetic dispersions

“…aentginosa in each of four cosmetic products containing different additives or not, either preserved or not with Ag' M or imidazolidinyl urea (0.6% w/w). As shown in Table I, and related to the base dispersion, the nonionic surfactants and the lipophilic material do not appear to interfere with Ag+ ions which kill the micro-organisms in 4 h and still guarantee this level of protection after 336 h. This agrees with previous results [25] showing that the microbicidal action of Ag' ions is not affected by the variable and doubtful composition of nonionic surfactants that, in this case, is conveniently represented by the polyoxyethylene ether derivatives of fatty alcohols (Emulgator 2 155) and by the polyethoxylated glycerol fatty acid ester (Tagat S). Furthermore, silver's efficacy appears to be little influenced by the complex moisturizer blend (Lactil) or protein (collagen).…”

“…This peculiarity could be advantageously employed to assure a more rapid drop in microbial concentration levels during product manufacture which normally requires a warm procedure. Lastly the use of anodic silver could be particularly recommended in 'leave-on' cosmetics because at active concentrations it does not cause any adverse reaction to the skin [25].…”

“…This device supplied, after 15 min, a solution of Ag' ~2 x lo-' M (PH M 7.6). The Ag' concentration was potentiometrically determined [25] using an AgzS electrode. Silver ion concentration was adjusted to lo-' M in each experiment.…”

“…Anodic silver is widely and successfully employed in disinfecting drinking water for mammalian consumption, at the recommended concentration of 10-6-10-5 M [24]. In a previous paper [25], to evaluate the presumptive indifference of Ag' ions in the formula, the microbicidal efficacy of this agent was investigated in aqueous solution containing nonionic surfactants and in some model dispersions. In these experiments, the microbicidal activity of Ag+ ions at 10T6 M was unaffected by lipophilic material and nonionic surfactants and good preservation was achieved against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus epidermidis and Candida albicans under severe conditions of contamination.…”