Mechanism of uptake of a cationic water-soluble pyridinium zinc phthalocyanine across the outer membrane of Escherichia coli

Previous studies have shown that a cationic water-soluble pyridinium zinc p hthalocyanine (PPC) is a powerful photosensitizer that is able to inactivat e Escherichia coli. In the current work incubation of E. coli cells with PP C in the dark caused alterations in the outer membrane permeability barrier of the cells, rendering the bacteria much more sensitive to hydrophobic co mpounds, with little effect seen with hydrophilic compounds. Addition of Mg 2+ to the medium prior to incubation of the cells with PPC prevented these alterations in the outer membrane permeability barrier. The presence of Mg2 + in the medium also prevented the photoinactivation of E. coli cells with PPC. These results are consistent with the hypothesis that PPC gains access across the outer membrane of E. coli cells via the self-promoted uptake pa thway, a mechanism of uptake postulated for the uptake of other cationic co mpounds across the outer membranes of gram-negative bacteria.