Mesosomal structures and antimicrobial activity induced by hemin oxidation or porphyrin photodynamic sensitization in Staphylococci

The porphyrin-dependent inactivation of Staphyloccocus aureus and the induction of mesosomal structures are described. The antimicrobial activity of different photoactivated porphyrins was compared with the dark cytotoxic effect of hemin. Deuteroporphyrin, protoporphyrin, hematoporphyrin, and hematoporphyrin derivative (Hpd) markedly reduced cell growth upon irradiation with light. Photofrin II, the polymerized fraction of Hpd, and other synthetic porphyrins had no effect on staphylococcal growth. Hemin immediately inhibited cell viability in the dark and induced the development of an irregular cell wall, analyzed by scanning electron microscopy (SEM). Inside the cytoplasm a multivesicular mesosome was formed near the septum, as detected by transmission electron microscopy (TEM). The mesosomal volume and its frequency in the cells was increased in a time-dependent manner. The mesosome appearance was not related to fixation by glutaraldehyde or to post-fixation by osmium tetroxide. Glycosyl moieties stained by ruthenium red revealed the formation of membrane-like structures in the mesosome. It is concluded that oxygen-dependent reactions potentiated by porphyrins may induce disturbances in the synthesis of staphylococcal membrane and cell wall, revealed as mesosomes.