Bactericidal Action of Photogenerated Singlet Oxygen from Photosensitizers Used in Plaque Disclosing Agents

Abstract

BackgroundPhotodynamic therapy (PDT) has been suggested as an efficient clinical approach for the treatment of dental plaque in the field of dental care. In PDT, once the photosensitizer is irradiated with light of a specific wavelength, it transfers the excitation energy to molecular oxygen, which gives rise to singlet oxygen.Methodology/Principal FindingsSince plaque disclosing agents usually contain photosensitizers such as rose bengal, erythrosine, and phloxine, they could be used for PTD upon photoactivation. The aim of the present study is to compare the ability of these three photosensitizers to produce singlet oxygen in relation to their bactericidal activity. The generation rates of singlet oxygen determined by applying an electron spin resonance technique were in the order phloxine > erythrosine ≒ rose bengal. On the other hand, rose bengal showed the highest bactericidal activity against Streptococcus mutans, a major causative pathogen of caries, followed by erythrosine and phloxine, both of which showed activity similar to each other. One of the reasons for the discrepancy between the singlet oxygen generating ability and bactericidal activity was the incorporation efficiency of the photosensitizers into the bacterial cells. The incorporation rate of rose bengal was the highest among the three photosensitizers examined in the present study, likely leading to the highest bactericidal activity. Meanwhile, the addition of L-histidine, a singlet oxygen quencher, cancelled the bactericidal activity of any of the three photoactivated photosensitizers, proving that singlet oxygen was responsible for the bactericidal action.ConclusionsIt is strongly suggested that rose bengal is a suitable photosensitizer for the plaque disclosing agents as compared to the other two photosensitizers, phloxine and erythrosine, when used for PDT.

Fungicidal effect of combined nano TiO2 with erythrosine for mediated photodynamic therapy on Candida albicans: an in vitro study

“…In a study by Ishiyama et al, erythrosine was also found to generate singlet oxygen when stimulated by 532 nm LED [16]. As expected, a high dose of erythrosine resulted in a higher antifungal effect, evidenced by a decrease in C. albicans by 0.86 log 10 and 1.85 log 10 (combined with TiO 2 ) as compared to the control treatment using 0.12% CHX.…”

Rose bengal uptake by E. faecalis and F. nucleatum and light-mediated antibacterial activity measured by flow cytometry

“…Because singlet oxygen is effective in the nanometer range (20 nm), photosensitizers that tightly bind or penetrate bacterial cells may elicit more antibacterial activity than those producing oxygen derivates nearby cells [14,16,33].…”

“…George et al [15] suggested that RB is a substrate of E. faecalis efflux-pumps, thereby supporting the intracellular incorporation of the dye. More recently, Ishiyama et al [16] investigated the incorporation and the 1 O 2 production of phloxine, erythrosine and RB in S. mutans suspensions. Despite a lower 1 O 2 production, RB displayed the highest incorporation rate and antibacterial activity among the three photosensitizers tested [16].…”

“…More recently, Ishiyama et al [16] investigated the incorporation and the 1 O 2 production of phloxine, erythrosine and RB in S. mutans suspensions. Despite a lower 1 O 2 production, RB displayed the highest incorporation rate and antibacterial activity among the three photosensitizers tested [16]. The relative porous layer of peptidoglycan surrounding the cytoplasmic membrane of Gram-positive bacteria was shown to allow the penetration of neutral or anionic PS's [17].…”

Microbicidal Activity of Artificially Generated Hydroxyl Radicals

“…This is a major advantage in comparison with antibiotics. Based on the bactericidal activity of PDT demonstrated by in vitro studies [28][29][30][31], the therapeutic effect of PDT following SRP has been studied expecting an additional effect. However, the clinical results are controversial between the studies [32][33][34][35].…”