The impact of antimicrobial photodynamic therapy in an artificial biofilm model

Abstract

The susceptibility of bacterial cultures in biofilm formations is important for a variety of clinical treatment procedures. Therefore, the aim of the study was to assess the impact of laser-induced antimicrobial photodynamic therapy on the viability of Streptococcus mutans cells employing an artificial biofilm model. Using sterile chambered coverglasses, a salivary pellicle layer was formed in 40 chambers. Streptococcus mutans cells were inoculated in a sterile culture medium. Employing a live/dead bacterial viability kit, bacteria with intact cell membranes stained fluorescent green. Each pellicle-coated test chamber was filled with 0.7 ml of the bacterial suspension and analysed using a confocal laser scanning microscope within a layer of 10 μm at intervals of 1 μm from the pellicle layer. Phenothiazine chloride was used as a photosensitizer in all 40 test chambers. A diode laser (wavelength 660 nm, output power 100 mW) was used to irradiated 20 chambers for 2 min. Fluorescence values in the test chambers after laser irradiation (median 2.1 U, range 0.4-3.4 U) were significantly lower than baseline values after adding the photosensitizer (median 3.6 U, range 1.1-9.0; p < 0.05). The non-irradiated control chambers showed no change in fluorescence at the end of an additional photosensitizer residence time of 2 min without laser irradiation (median 1.9 U, range 0.7-3.6; median 1.9 U, range 0.8-6.0, respectively; p > 0.05). The present study indicated that laser irradiation is an essential part of antimicrobial photodynamic therapy to reduce bacteria within a layer of 10 μm. Further studies are needed to evaluate the maximum biofilm thickness that still allows a toxic effect on microorganisms.

Novel Broad-Spectrum Antimicrobial Photoinactivation of In Situ Oral Biofilms by Visible Light plus Water-Filtered Infrared A

“…This suggests that a posttreatment decrease in green fluorescence signals can be proportionally attributed to photosensitizer incorporation within the bacterial cells rather than to competitive inhibition, namely, the interference of TB or Ce6 with the binding of the live/dead dyes to intracellular targets. A similar tendency was also shown in several in vitro reports concerning the application of various APDT methods and photosensitizers to bacteria (51)(52)(53). Nevertheless, Pfitzner et al interpreted their contradictory results as resulting from the presence of fluorescent photosensitizers, which possibly make the measured number of nonvital microorganisms stained with SYTO 9 -PI inaccurate (46).…”

Photodynamic antimicrobial effect of safranine O on an ex vivo periodontal biofilm

“…As it is known, bacteria in a biofilm are better protected from antimicrobial approaches. In a recent publication by Schneider et al the penetration of an ex vivo biofilm by the PS phenothiazine chloride was observed. It was found, that there is a decrease in available PS from the top to the bottom of the biofilm.…”

Photodynamic therapy in dentistry: a literature review

“…Moreover, recent studies have reported that photodynamic therapy induced bacterial cell killing and reduced bacterial numbers by more than tenfold in S. mutans, Streptococcus sobrinus, and Streptococcus sanguinis biofilms when toluidine blue O or erythrosine was used as the photosensitizer [82][83][84][85]. Schneider et al [86] assessed the effect of laser-induced antimicrobial photodynamic therapy on the viability of S. mutans cells employing an artificial biofilm model and concluded that laser irradiation is an essential part of antimicrobial photodynamic therapy to reduce bacteria within a layer of 10 μm.…”