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

Rose Bengal (RB) is a halogenated xanthene dye that has been used to mediate antimicrobial photodynamic inactivation for several years. While highly active against Gram-positive bacteria, RB is largely inactive in killing Gram-negative bacteria. We have discovered that addition of the non-toxic salt potassium iodide (100mM) potentiates green light (540nm)-mediated killing by up to six extra logs with Gram-negative bacteria Escherichia coli and Pseudomonas aeruginosa, Gram-positive methicillin resistant Staphylococcus aureus, and 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 killing in three different scenarios: (1) cells+RB+KI are mixed together then illuminated with green light; (2) cells+RB are centrifuged then KI added then green light; (3) RB+KI+green light then cells added after light. We also showed that KI could potentiate RB-PDT in a mouse model of skin abrasions infected with bioluminescent P. aeruginosa.

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