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.

Meso-substituted cationic porphyrins as efficient photosensitizers of gram-positive and gram-negative bacteria.

Previous studies on the photosensitization of bacterial cells with different neutral or negatively charged porphyrins and phthalocyanines have demonstrated that, although Gram-positive bacteria are efficiently photoinactivated, Gram-negative bacteria become photosensitive only after modification of the permeability of their outer membrane. The results described in this paper show that two meso-substituted cationic porphyrins, namely tetra(4N-methyl-pyridyl)porphine tetraiodide and tetra(4N,N,N-trimethyl-anilinium)porphine, efficiently photosensitize the inactivation of Gram-negative bacteria, such as Vibrio anguillarum and Escherichia coli. A negatively charged meso-substituted porphyrin, tetra(4-sulphonatophenyl)porphine, has no appreciable photosensitizing activity towards Gram-negative bacteria, although all three porphyrins exhibit a similar subcellular distribution pattern, being mainly localized in the protoplasts or spheroplasts. Moreover, the three porphyrins show similar efficiency in the photoinactivation of the Gram-positive bacterium Entorecoccus seriolicida.

Studies on the mechanism of bacteria photosensitization by meso-substituted cationic porphyrins.

Cationic porphyrins have been shown to photoinduce the direct inactivation of Gram-positive (G+) and Gram-negative (G-) bacteria, thereby differing from anionic or neutral porphyrins which can photosensitize the G- bacteria only after permeabilization of their outer membrane. The present data show that the differences between these positively and negatively charged porphyrins are not related by a difference in the intrinsic photosensitizing efficiency, as determined by the photo-oxidation of model substrates or the yield of 1O2 generation; moreover, there are only minor differences in the quantum yield of porphyrin photobleaching. Rather, it appears that the positive charge promotes an electrostatic binding of the porphyrin to the outer cell surface inducing an initial limited damage which favours the penetration of the photosensitizer. Actually, the overall photoprocess is inhibited by the preincorporation of the porphyrin into liposomes, while it is enhanced by using amphiphilic dicationic porphyrins which bind to endocellular sites in larger amounts and in a more stable form.