Potassium iodide potentiates antimicrobial photodynamic inactivation mediated by Rose Bengal: in vitro and in vivo studies

Abstract

Rose bengal (RB) is a halogenated xanthene dye that has been used to mediate antimicrobial photodynamic inactivation for several years. While RB is highly active against Gram-positive bacteria, it is largely inactive in killing Gram-negative bacteria. We have discovered that addition of the nontoxic salt potassium iodide (100 mM) potentiates green light (540-nm)-mediated killing by up to 6 extra logs with the Gram-negative bacteria Escherichia coli and Pseudomonas aeruginosa, the Gram-positive bacterium methicillin-resistant Staphylococcus aureus, and the fungal yeast Candida albicans. The mechanism is proposed to be singlet oxygen addition to iodide anion to form peroxyiodide, which decomposes into radicals and, finally, forms hydrogen peroxide and molecular iodine. The effects of these different bactericidal species can be teased apart by comparing the levels of killing achieved in three different scenarios: (i) cells, RB, and KI are mixed together and then illuminated with green light; (ii) cells and RB are centrifuged, and then KI is added and the mixture is illuminated with green light; and (iii) RB and KI are illuminated with green light, and then cells are added after illumination with the light. We also showed that KI could potentiate RB photodynamic therapy in a mouse model of skin abrasions infected with bioluminescent P. aeruginosa.

Effects of Rose Bengal‐ and Methylene Blue‐Mediated Potassium Iodide‐Potentiated Photodynamic Therapy on Enterococcus faecalis: A Comparative Study

“…2). The enhancing effect of KI observed in the present study corresponded to the effects reported by Vecchio et al [25] and Wen et al [24]. At the chosen light dose (6 J/cm 2 ), based on clinical and mechanical considerations, MB (0.4 μM) or RB (0.2 μM) plus KI (100 mM) and light eradicated E. faecalis.…”

“…Potassium iodide (KI), a nontoxic inorganic salt, has been shown to exhibit potentiating activities on antimicrobial PDT to avoid adverse effects and staining problems [22][23][24][25]. Vecchio et al [25] reported that photodynamic inactivation using MB (10 μM) as a PS and KI (10 mM) as a potentiator could eradicate Staphylococcus aureus with an irradiation time of 50 seconds and an irradiance of 100 mW/cm 2 .…”

“…Wen et al [24] reported that RB antimicrobial PDT at a concentration of only 0.1 μM potentiated by 100 mM KI could result in bacterial eradication because Gram‐positive bacteria are very susceptible to antimicrobial PDT with anionic PS. In addition, antimicrobial PDT with certain concentrations of RB and irradiation with blue light (380–500 nm) for 240 seconds showed an apparent bactericidal effect without damaging the stem cells, such as human embryonic stem cells, odontoblast‐like cells, and undifferentiated dental pulp cells [28].…”

Comparison of the effect of ethanol and potassium iodide in antibacterial photodynamic therapy on gram negative pathogens

“…Purpose of using KI was to increase effectiveness of PS for the production of more radical ions. For this reason, 100 mM KI concentration was chosen as an optimum parameter after literature survey [16][17][18][19]. When the effects of only KI and KI together with Ce6 were studied, the results showed that they had no lethal effects on the bacteria.…”

“…It has been shown that the mechanism of action of KI involves electron transfer reactions to produce iodine and molecular radicals [16]. KI could also potentiate aPDT to produce more reactive species [17]. This reaction seems to have singlet oxygens to produce peroxy iodide, which is subsequently converted into molecular iodine and hydrogen peroxide.…”