Photosensitizing activity of hematoporphyrin on Staphylococcus aureus cells

The photosensitizing action of hematoporphyrin (Hp) on two Staphylococcus aureus strains was investigated to determine if the photoprocess induces in vivo damage in DNA in addition to that occurring at the level of the cytoplasmic membrane. The results obtained demonstrate that the photokilling is dependent on the Hp dose even though the two strains, having a similar Hp-binding capacity, show different levels of photosensitivity. The electrophoretic analysis of cytoplasmic membrane proteins and DNA (chromosomal and plasmidial) suggests that the membrane represents the primary target of the photoprocess, while the DNA, that is damaged both in vivo and in vitro only at relatively long irradiation time, might be a secondary target. Moreover, the photoprocess results in mutagenesis for Salmonella typhimurium tester strains. This information is particularly important in view of the potential use of photodynamic therapy for the treatment of microbial infections.