Killing mechanism of bacteria within multi-species biofilm by blue light

Abstract

Objectives: The aim of the study was to characterize the immediate and delayed effects of non-coherent blue-light treatment on the composition and viability of an in vitro biofilm composed of anaerobic multispecies, as well as the mechanisms involved. Methods: A multispecies biofilm was constructed of Streptococcus sanguinis, Actinomyces naeslundii, Porphyromonas gingivalis and Fusobacterium nucleatum, test groups were exposed to blue light. The multispecies biofilm was explored with a newly developed method based on flow cytometry and confocal microscopy. The involvement of the paracrine pathway in the phototoxic mechanism was investigated by a crossover of the supernatants between monospecies P. gingivalis and F. nucleatum biofilms. Results: Blue light led to a reduction of about 50% in the viable pathogenic bacteria P. gingivalis and F. nucleatum, vs that in the non-exposed biofilm. Biofilm thickness was also reduced by 50%. The phototoxic effect of blue light on mono-species biofilm was observed in P. gingivalis, whereas F. nucleatum biofilm was unaffected. A lethal effect was obtained when the supernatant of P. gingivalis biofilm previously exposed to blue light was added to the F. nucleatum biofilm. The effect was circumvented by the addition of reactive oxygen species (ROS) scavengers to the supernatant. Conclusion: Blue-light has an impact on the bacterial composition and viability of the multispecies biofilm. The phototoxic effect of blue light on P. gingivalis in biofilm was induced directly and on F. nucleatum via ROS mediators of the paracrine pathway. This phenomenon may lead to a novel approach for 'replacement therapy,' resulting in a less periodontopathogenic biofilm. ARTICLE HISTORY

Interdental Plaque Microbial Community Changes under In Vitro Violet LED Irradiation

“…One of the reasons for this change in the diversity of dental plaque microbiota may be the decrease in the proportion of Fusobacterium species in the community. This is consistent with the results of a previous experiment, in which multispecies biofilms were irradiated with blue light (142 J/cm 2 ) [29]. In the current study, F. periodonticum and F. nucleatum were highly sensitive to violet LED irradiation, regardless of their subspecies classification.…”

“…In fact, medical lasers are currently being investigated to treat infectious oral diseases [ 25 , 26 , 27 ]. Much scientific evidence has also confirmed the bactericidal efficacy of several individual types of visible light on periodontal pathogens, even without the presence of exogenous photoactivated compounds [ 28 , 29 , 30 , 31 , 32 ]. Moreover, blue light (400–500 nm) affects the bacterial composition and viability of microbial biofilms in vitro, including Porphyromonas gingivalis, Prevotella species, Fusobacterium nucleatum subspecies, Fusobacterium periodonticum, Streptococcus sanguinis , and Actinomyces naeslundii [ 28 , 29 ].…”

“…Much scientific evidence has also confirmed the bactericidal efficacy of several individual types of visible light on periodontal pathogens, even without the presence of exogenous photoactivated compounds [ 28 , 29 , 30 , 31 , 32 ]. Moreover, blue light (400–500 nm) affects the bacterial composition and viability of microbial biofilms in vitro, including Porphyromonas gingivalis, Prevotella species, Fusobacterium nucleatum subspecies, Fusobacterium periodonticum, Streptococcus sanguinis , and Actinomyces naeslundii [ 28 , 29 ]. More specifically, relatively short wavelengths of light close to 405 nm, which are typically defined as the violet range of visible light, have exhibited a bactericidal effect on selected medically important Gram-positive and Gram-negative bacteria [ 30 , 31 , 32 ].…”

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