ABSTRACT
Photodynamic activity of chemical compounds against microorganisms was first published more than 100 years ago. Oskar Raab observed that toxicity of acridine hydrochloride against Paramecium caudatum was dependent on the amount of light that was incident on the experimental mixture. In addition, his teacher, Hermann von Tappeiner, reported that the toxic effects in the presence of light are not a result of heat. Afterwards, von Tappeiner termed the influence of light and oxygen in combination with a nontoxic dye as a “photodynamic reaction.” Additional investigations demonstrated the involvement of oxygen in killing bacteria because the antibacterial activity of fluorescent dyes against the facultative anaerobic species Proteus vulgaris could not be demonstrated in the absence of oxygen.
