Modulation of the UVB-induced lethality by furocoumarins in Staphylococcus aureus

Furocumarins (FCs) are photoactive compounds capable of binding to DNA, and once excited by UVA light (∼365 nm), they form photoadducts which can lead to mutagenicity and lethality. However, the biological effects of FCs combined with UVB light (312 nm) is still little investigated. In the present study, the lethal effect of UVB light alone and combined with different concentrations of 8-methoxypsoralen (8-MOP), 4,5′,8-trimethylpsoralen (TMP) and 3-carbethoxypsoralen (3-CPs) was evaluated in a strain of Staphylococcus aureus. 8-MOP-UVB and TMP-UVB were more effective in inducing lethality compared to UVB alone, indicating that these FCs act as photosensitizing agents for UVB. The increase in concentration of 8-MOP resulted in a greater mortality. On the contrary, a decrease in mortality was found with an increase in TMP concentration. 3-CPs protected bacteria against damage induced by UVB, which can be attributed to the inhibition of cyclobutyl pyrimidine dimer formation. The different modulatory effects on lethality induced by UVB shown by the FCs tested could be related to differences in the specificity of each compound for particular nucleotide sequences, as well as other chemical characteristics of each molecule could influence the number and types of adducts formed, contributing to the photosensitizing or photoprotective effects observed.