Effect of phototoxic substances on simple biological systems. I. Standardizing the method with furocoumarins

: As a basis for the investigation of new substances in respect of their photosensitization effects, we established and standardized 3 microbiological test systems, which enabled us to do without animal experiments. Using several furocumarines and various sources of light, we performed a comparative study on the eukaryotes, Chlamydomonas reinhardii (CR) and Candida albicans, and the prokaryote, Bacillus subtilis. We found that, if different light qualities were employed, our test systems also allowed a comparison of different substances by means of half-quantitative evaluation of the inhibiting areolas, which appear after exposure. With regard to the furocumarines, 8- and 5-methoxypsoralene (MOP) had the strongest photosensitizing effect under all test conditions. The remaining furocumarines showed decreasing effectiveness from psoralene to trimethylpsoralene (TMP) and imperatorine; psoralene, however, was slightly more effective in CR than 5-MOP. With the exception of CR, TMP had a stronger effect on the micro-organisms than imperatorine.