Photodynamic inactivation of E. coli by rose bengal immobilized on polystyrene beads.

Abstract. The photodynamic inactivation of E. coli by visible light and O2 was found to occur in the presence of the sensitizer rose bengal, immobilized by covalent bonding to polystyrene beads. The demonstrated absence of significant amounts of dissolved rose bengal indicated that an inactivation mechanism based on penetration of sensitizer molecules into the cell's interior could not be operating. Survival curves typically exhibited induction periods followed by rapid exponential death, with 99.99% kill requiring 1–2 h depending on conditions. A mechanism involving the participation of photo-generated singlet excited oxygen O2(1δ) in inactivation of E. coli is proposed. The photodynamic inactivation rate increased significantly in H2O compared with H2O, which is evidence supporting singlet oxygen as an active intermediate, since O2(1δ) has a much longer lifetime in H2O than in H2O. H2O did not act as a short term poison in the absence of sensitizer.