On the Relation between Photodynamic Activities and Photochemical Oxidation in Xanthene Dyes

Xanthene dyes such as erythrosine, eosine, phloxine, rose bengale when exposed to visible light have lethal effects on bacteria at concentrations at which the bacteria can still duplicate in the absence of light.Y. Kurayuki et al. have reported on the formation of resorcinol, phthalic acid and other decomposed products in the fading solution of xanthene dye exposed to daylight. But in our experiments the lethal activities of those decomposed products on bacteria were negligible. And as the photodynamic activities in xanthene dyes as well as methylene blue and proflavine can be found only in aerobic condition, the photodynamic effects on bacteria presumably are due to the oxidation of some component of bacterial cell. This mechanism is simillar to that of photochemical oxidation reported by G. Oster et al.