Photo Inactivation of Streptococcus mutans Biofilm by Violet-Blue light

Abstract

Among various preventive approaches, non-invasive phototherapy/photodynamic therapy is one method used to control oral biofilm. Studies indicate that light at specific wavelengths has a potent antibacterial effect. The objective of this study was to determine the effectiveness of violet-blue light at 380-440 nm to inhibit biofilm formation of Streptococcus mutans or kill S. mutans. S. mutans UA159 biofilm cells were grown for 12-16 h in 96-well flat-bottom microtiter plates using Tryptic Soy broth (TSB) or TSB with 1% sucrose (TSBS). Biofilm was irradiated with violet-blue light for 5 min. After exposure, plates were re-incubated at 37°C for either 2 or 6 h to allow the bacteria to recover. A crystal violet biofilm assay was used to determine relative densities of the biofilm cells grown in TSB, but not in TSBS, exposed to violet-blue light. The results indicated a statistically significant (p < 0.05) decrease compared to the nontreated groups after the 2 or 6h recovery period. Growth rates of planktonic and biofilm cells indicated a significant reduction in the growth rate of the violet-blue light-treated groups grown in TSB and TSBS. Biofilm viability assays confirmed a statistically significant difference between Violet-blue light-treated and non-treated groups in TSB and TSBS. Visible Violet-blue light of the electromagnetic spectrum has the ability to inhibit S. mutans growth and reduce the formation of S. mutans biofilm. This in-vitro study demonstrated that Violet-blue light has the capacity to inhibit S. mutans biofilm formation. Potential clinical applications of light therapy in the future remain bright in preventing the development and progression of dental caries.

Antimicrobial blue light inactivation of pathogenic microbes: State of the art

“…Another study of aBL inactivation of S. mutans biofilm was carried out by Gomez et al (Gomez et al, 2016). In the study, biofilms cultured in 96-well microtiter plates were exposed to aBL (380–440 nm, peak emission 405 nm) at an exposure of 9.26 J/cm 2 .…”

Antimicrobial Efficacy of Irradiation with Visible Light on Oral BacteriaIn Vitro: A Systematic Review

“…In another study, Gomez et al irradiated initial biofilms (λ = 380-440 nm with 405-nm peak) formed by strains of S. mutans grown for 12-16 h [35]. Intensity on surface was 13 mW/cm 2 and irradiation was done for 5 min, resulting in a fluence of 9.26 J/cm 2 .…”

Effect of phototherapy on the metabolism of <i>Streptococcus mutans</i> biofilm based on a colorimetric tetrazolium assay

“…In our previous study, we demonstrated photoinactivation of S. mutans with 5 min of violet-blue light treatment by quantitatively determining the viability (colony-forming units) of biofilm cells (15). In this study, we found decreased metabolic activity of violet-blue light-treated S. mutans at 0-h and 2-h recovery periods, providing an indirect estimation of cell viability.…”

“…The metabolic activity of TSBS S. mutans remained unaffected after 6-h recovery period and was increased compared with 0-h recovery period. We previously reported that there was no difference in biofilm formation with respect to light treatment after the 6-h reincubation period in the TSBS group, which suggests that the bacterial cells are viable (15). Bacterial cells, however, which are encompassed within extracellular glucans, may be improperly reduced by tetrazolium salts (19) in the assay used in this study.…”

“…Whereas a delayed antibacterial effect (12,13) was reported by Feuerstein et al (11) in an S. mutans biofilm grown for 6 h, whereas Chebath et al (14) observed increased antibacterial effect after 3-, 5-, 7-, and 10-min treatment (13). Photoinactivation of S. mutans biofilm has been achieved through a 5-min treatment with violet-blue light with a peak wavelength of 405 nm (15). This study reported the effect of violet-blue light on biofilm formation, colony forming units, and growth kinetics of S. mutans.…”