A Study of the Uptake of Toluidine Blue O by Porphyromonas gingivalis and the Mechanism of Lethal Photosensitization

Abstract

The purpose of the study was to determine the distribution of the photosensitizer toluidine blue O (TBO) within Porphyromonas gingivalis and the possible mechanism(s) involved in the lethal photosensitization of this organism. The distribution of TBO was determined by incubating P. gingivalis with tritiated TBO (3H-TBO) and fractionating the cells into outer membrane (OM), plasma membrane (PM), cytoplasmic proteins, other cytoplasmic constituents and DNA. The percentage of TBO in each of the fractions was found to be, 86.7, 5.4, 1.9, 5.7 and 0.3%, respectively. The involvement of cytotoxic species in the lethal photosensitization induced by light from a heliumneon (HeNe) laser and TBO was investigated by using deuterium oxide (D2O), which prolongs the lifetime of singlet oxygen, and the free radical and signlet oxygen scavenger L-tryptophan. There were 9.0 log10 and 2 log10 reductions in the presence of D2O and H2O (saline solutions), respectively, at a light dose of 0.44 J (energy density = 0.22 J/cm2), suggesting the involvement of singlet oxygen. Decreased kills were attained in the presence of increasing concentrations of L-tryptophan. The effect of lethal photosensitization on whole cell proteins was determined by measuring tryptophan fluorescence, which decreased by 30% using 4.3 J (energy density = 4.3 J/cm2) of light. Effects on the OM and PM proteins were determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis. There was evidence of change in the molecular masses of several PM proteins and OM proteins compared to controls. There was evidence of damage to the DNA obtained from irradiated cells. Scanning electron microscopic studies showed that there was coaggregation of P. gingivalis cells when sensitized and then exposed to laser light. These results suggest that lethal photosensitization of P. gingivalis may involve changes in OM and/or PM proteins and DNA damage mediated by singlet oxygen.

Gold nanoparticles enhance methylene blue– induced photodynamic therapy: a novel therapeutic approach to inhibit Candida albicans biofilm

“…21 Photosensitizer thiazine dyes such as methylene blue (MB), toluidine blue O (TBO), and pthalocyanine have been shown to be phototoxic against Pseudomonas aeruginosa and Porphyromonas gingivalis biofilm. [22][23][24] Recently, it has also been reported that MB also has fungicidal effects against C. albicans. 18,19 Colloidal gold nanoparticles (GNPs) have resilient properties compared to other inorganic nanoparticles, such as unique plasmon-resonance optical properties and a bioconjugation surface for molecular probes.…”

Susceptibility of microcosm subgingival dental plaques to lethal photosensitization

“…With PDT, lethal photosensitization mediates bacterial killing via singlet oxygen and free radicals. Resistance development would be unlikely owing to the multiplicity of target sites, which include the outer and plasma membranes of Gramnegative bacteria, DNA and photolabile surface-associated proteins (Bhatti et al, 1998(Bhatti et al, , 2001, against which the generated singlet oxygen and free radicals are active.…”

Evaluation of the Practicality of Melanin as a Photodynamic-Inactivation Photosensitizer by Its Nanonization

“…In PDI, a photosensitizer is used to turn molecular oxygen into singlet oxygen 1 O 2 upon irradiation with light. The singlet oxygen produced and other ROS evolved from it subsequently have microbicidal ability, as a result of their strong oxidative power which leads to damage of vital molecules or organelles of microbes [10][11][12]. It is well established that free radicals, being also strongly oxidative, express similar microbicidal activity [13].…”