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. 2020 Jan:203:111730.
doi: 10.1016/j.jphotobiol.2019.111730. Epub 2019 Dec 16.

Potassium iodide enhances the photobactericidal effect of methylene blue on Enterococcus faecalis as planktonic cells and as biofilm infection in teeth

Lintian Yuan  1 , Peijun Lyu  1 , Ying-Ying Huang  2 , Ning Du  3 , Wei Qi  4 , Michael R Hamblin  5 , Yuguang Wang  6
Affiliations

Potassium iodide enhances the photobactericidal effect of methylene blue on Enterococcus faecalis as planktonic cells and as biofilm infection in teeth

Lintian Yuan et al. J Photochem Photobiol B. 2020 Jan.

Erratum in

Abstract

Objective: To explore the effectiveness, biosafety, photobleaching and mechanism of antimicrobial photodynamic therapy (aPDT) using methylene blue (MB) plus potassium iodide (KI), for root canal infections.

Methods: Different combinations and concentrations of MB, KI and 660 nm LED light were used against E. faecalis in planktonic and in biofilm states by colony-forming unit (CFU), confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM). Human gingival fibroblasts (HGF) were used for safety testing by Cell Counting Kit-8 (CCK8) and fluorescence microscopy (FLM). The photobleaching effect and mechanisms were analyzed.

Results: KI could not only enhance MB aPDT on E. faecalis in both planktonic and biofilm states even in a hypoxic environment, but also produced a long-lasting bactericidal effect after end of the illumination. KI could accelerate photobleaching to reduce tooth staining by MB, and the mixture was harmless for HGFs. Mechanistic studies showed the generation of hydrogen peroxide and free iodine, and iodine radicals may be formed in hypoxia.

Conclusion: aPDT with MB plus KI could be used for root canal disinfection and clinical studies are worth pursuing.

Keywords: Antimicrobial photodynamic inactivation; Enterococcus faecalis; Methylene blue; Potassium iodide; Root canal disinfection.

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Conflict of interest statement

Conflicts of interest

Figures

Figure 1
Figure 1. Spectrum of 660 nm deep red led light source
(Data taken from Thorlabs.com).
Figure 2
Figure 2. MB plus KI enhanced aPDT of E. faecalis.
(A) KI (100mM) reduced MB concentration needed for E. faecalis aPDT using 6 J/cm2. (B) KI concentration effect on potentiation of MB (0.1 or 0.4μM) aPDT using 6 J/cm2. (C) KI (100mM) reduces light dose needed for E. faecalis MB (0.1–0.4μM)-aPDT. (D) MB plus KI aPDT for E. faecalis sampled at different time after the end of illumination. (E) Hypoxic antimicrobial effect of MB (0.4μM) plus KI (100mM) aPDT for E. faecalis using 6J/cm2. (F) Photoactivation of MB with or without KI to kill E. faecalis biofilm at 30 J/cm2 of light, the biofilms were formed in 6 well plates. (*P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001).
Figure 3.
Figure 3.. CLSM images for E. faecalis biofilm growing on dentin blocks.
Biofilm were treated after 21 days using the following groups. (A1-A3) Control group; (B1-B3) MB (10 μM) plus 30 J/cm2; (C1-C3) MB (10 μM) plus KI (100 mM) plus 30 J/cm2. Images are representative examples of three separate images
Figure 4
Figure 4. SEM images of E. faecalis biofilm.
(A) Control group; (B) MB (10 μM) plus 30 J/cm2; (C) MB (10 μM) plus KI (100 mM) plus 30 J/cm2. Images are representative examples of three separate images
Figure 5
Figure 5
Light-induced color changes of MB ± KI with or without 6 J/cm2.
Figure 6
Figure 6. Survival fractions of HGFs.
Untreated control group; MB (2 μM) plus 6 J/cm2 light: MB (0.4 μM) plus KI (100 mM) plus 6 J/cm2 light; NaClO (5.25%)
Figure 7
Figure 7. Fluorescence microscopic images for HGF cells in groups.
(A1-A3) untreated group; (B1-B3) MB (2 μM) + 6 J/cm2; (C1-C3) MB (0.4 μM) + KI (100 mM) + 6 J/cm2; (D1-D3) 5.25% NaClO. A1-D1, green cells are living cells; A2-D2, red cells are dead cells; A3-D3 are merged image.
Figure 8
Figure 8. Mechanistic experiments.
A) Production of free iodine measured by starch indicator assay. B) Production of hydrogen peroxide by Amplex red assay. C) Production of superoxide anion by the NBT test.
See this image and copyright information in PMC

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