Photoinactivation of F. nucleatum and P. gingivalis using the ruthenium-based RD3 sensitizer and a conventional halogen lamp

Abstract Objective The photodynamic therapy (PDT) is an alternative method to suppress oral pathogens by the activation of a photosensitizer with laser light. The aim of this study was to investigate the phototoxic effect of three ruthenium-based photosensitizers on Fusobacterium nucleatum and Porphyromonas gingivalis. Methods In this in vitro study F. nucleatum and P. gingivalis were incubated with three photosensitizers: (i) a hydrophobic tris-(4,7-diphenyl-1,10-phenanthroline)-ruthenium(II)-dication (RD3), (ii) a hydrophilic tris-[(1,10-phenanthroline-4,7-diyl)-bis-(benzenesulfonato)]-ruthenate tetra-anion (RSD3) and (iii) a lower hydrophilic tris-(2,2′-bipyridine)-ruthenium(II) dication (RBY). The subsequent irradiation was done with blue-band halogen light (450–485 nm) for 20 s using a conventional polymerizer. Control samples consisted of bacterial cell suspension irradiated and non-irradiated in the absence of photosensitizer or incubated with the photosensitizer without irradiation. Bacterial inactivation was determined by the numbers of colony-forming units (cfu/ml) after anaerobic cultivation. Results The RD3 photosensitizer reduced the viability of F. nucleatum by 4-log 10 and of P. gingivalis completely after irradiation for 20 s. The viability loss correlated significantly with the concentration of the RD3 photosensitizer and reached a peak at a concentration of 12.5 μM ( p < 0.05). The RSD3 and RBY photosensitizers had distinctly lower phototoxic effects in comparison to RD3. Conclusion The RD3 photosensitizer showed a phototoxic effect on F. nucleatum and P. gingivalis . The results suggest that the application of the RD3 photosensitizer under visible light may be helpful as an adjunct treatment approach to the inactivation of periodontopathogenic bacteria.