SILVER-NITRATE - ANTIMICROBIAL ACTIVITY RELATED TO CYTOTOXICITY IN CULTURED HUMAN FIBROBLASTS

The aims of this study were to ascertain whether silver nitrate (AgNO3 ) concentrations below those used in clinical practice inhibit bacteri al growth, and in parallel study the cytotoxic effects on human fibrob lasts. The cytoprotective effects of fetal calf serum (FCS) were also evaluated, The cytotoxic effects of Fight different silver nitrate con centrations R-ere determined by assessing mitochondrial activity of vi able cells capable of cleaving tetrazolium salts. Antimicrobial activi ty of AgNO3, range: 7-550 x I0(-5) %, was tested against Staphylococcu s aureus, Citrobacter freundii, and Pseudomonas aeruginosa. Silver nit rate concentrations exerting antimicrobial effects were: S. aureus, >7 0 x 10(-5) %; P. aeruginosa, greater than or equal to 270 x 10(-5) %, and C. freundii, greater than or equal to 550 x 10(-5) %. With 2% FCS, the lowest AgNO3 concentration studied(7 x 10(-5) %) showed cytotoxic effects (cell survival 71 +/- 19%) at only 2 h of incubation. Under t hese conditions AgNO3 cytotoxicity was time- and concentration-depende nt in all exposure periods. Cytotoxicity was greatly enhanced causing 76% fibroblast growth inhibition ar concentrations of 14 x 10(-5) % an d contact lime of 2 h, The AgNO3 concentration of 7 x 10(-5) % was als o cytotoxic with 5% FCS in the media compared with controls, although cell survival was higher than with 2% FCS. The cytoprotective action o f FCS was clearly shown at the concentration of 10% at which AgNO3 cyt otoxicity of 7 x 10(-5) % to 28 x 10(-5) %, was partially or completel y inhibited. Our results show that AgNO3 at concentrations 100-700 tim es more diluted than that normally used in clinical practice retained effective inhibitory activity against some of the above-mentioned micr oorganisms. However, even these concentrations are cytotoxic far cultu red fibroblasts. Thus, silver nitrate concentrations up to 100 times m ore diluted can be used, since they possess bacterial growth-inhibitin g power, are less cytotoxic and therefore favour wound healing.