The activity of singlet-oxygen sensitizers for photodynamic inactivation (PDI) of microorganisms and photodynamic therapy of tumor cells has been evaluated using Escherichia coli, Saccharomyces cerevisiae, and human cancer cell lines. In this chapter, drug resistance of E. coli was examined based on the PDI activity of a variety of RPy-P-porphyrin sensitizers with different number of ionic valence and different hydrophobic characters. The PDI activities toward E. coli were evaluated using the minimum effective concentrations ([P]) of the porphyrin sensitizers. It was found that the [P] value for E. coli was larger than that for S. cerevisiae. E. coli has drug-resistance toward hydrophobic and mono-cationic porphyrins. However, E. coli has weak drug-resistance toward the porphyrins with both polycationic character and hydrophobicity. Since the outer membrane mainly consists of lipopolysaccharides and phospholipids that are negatively charged, cationic porphyrins are able to adsorb to the outer leaflet. Then the cationic porphyrins with hydrophobic character can interact with not only the outer leaflet but also inner leaflet of the outer membrane and the plasma membrane. Thus, porphyrins may be incorporated inside E. coli cells via the self-promoted uptake pathway. Moreover, polycationic porphyrins can interact with DNA and proteins by strong binding affinities.
Part of the book: The Universe of Escherichia coli