The binding and photosensitization effects of tetrabenzoporphyrins and texaphyrin in bacterial cells

A new class of photosensitizers which inactivate efficiently Gram-positive bacterial cells is described. The photosensitizers used in this study were Mg and Zn-tetrabenzoporphyrin (MgTBP and ZnTBP), which possess strong absorption bands at 630 nm and Cd-texaphyrin (CdTX), whose longest absorption band is at 770 nm. These sensitizers thus have optical properties that are superior to those of haematoporphyrin. It is demonstrated that MgTBP and CdTX have similar photosensitizing efficiencies as haematoporphyrin on Gram-positive Staphylococcus aureus cells but are better on the Gram-negative Escherichia coli in the presence of polymyxin nonapeptide, a membrane permeabilizing material. It seems, from the elemental content of the photosensitized Gram-positive and Gram-negative bacterial cells, that there is a difference in the killing mechanism of haematoporphyrin as compared to that of MgTBP or CdTX.