Protective effect of furocoumarins against 254-nm ultraviolet in Staphylococcus aureus.

For Staphylococcus aureus, pretreatment with furocoumarins (FCs) protect cells against killing by far ultraviolet light (FUV; approximately 254 nm). This protective effect was evident in the repair-proficient, parental strain as well as in the repair-deficient variants in the following order of efficacy: 4,5'',8-trimethylpsoralen << 8-methoxypsoralen congruent with angelicin < 3-carbethoxypsoralen. The extent of protection was greater in the parental strain, indicating that despite the protective effect, a certain number of lethal lesions are nevertheless produced, which would be repaired with greater efficiency in such a strain than in the repair-deficient ones. This protective effect could be attribute to the inhibition of the formation of cyclobutyl pyrimidine dimers. Although the energy-transfer concept could explain the inhibition of pyrimidine dimer formation, and thus the protective effect of FC against FUV, we cannot rule out the possibility that the differences in degree of protection afforded by the FC employed here are related to a subtle and complex combination of effects.