title: Bacterial photodynamic inactivation mediated by methylene blue and red light is enhanced by synergistic effect of potassium iodide.
abstract: The inexorable increase of antibiotic resistance occurring in different bacterial species is increasing the interest in developing new antimicrobial treatments that will be equally effective against multidrug-resistant strains and will not themselves induce resistance. One of these alternatives may be photodynamic inactivation (PDI), which uses a combination of nontoxic dyes, called photosensitizers (PS), excited by harmless visible light to generate reactive oxygen species (ROS) by type 1 (radical) and type 2 (singlet oxygen) pathways. In this study, we asked whether it was possible to improve the efficacy of PDI in vitro and in vivo by addition of the inert salt potassium iodide (KI) to a commonly investigated PS, the phenothiazinium dye methylene blue (MB). By adding KI, we observed a consistent increase of red light-mediated bacterial killing of Gram-positive and Gram-negative species in vitro and in vivo. In vivo, we also observed less bacterial recurrence in wounds in the days posttreatment. The mechanism of action is probably due to formation of reactive iodine species that are produced quickly with a short lifetime. This finding may have a relevant clinical impact by reducing the risk of amputation and, in some cases, the risk of death, leading to improvement in the care of patients affected by localized infections.
authors.affiliation: Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, Massachusetts, USA Department of Dermatology, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Daniela
authors.initials: D
authors.lastname: Vecchio
authors.affiliation: Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, Massachusetts, USA Department of Dermatology, Harvard Medical School, Boston, Massachusetts, USA Defence Institute of Physiology and Allied Sciences (DIPAS), Delhi, India.
authors.forename: Asheesh
authors.initials: A
authors.lastname: Gupta
authors.affiliation: Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, Massachusetts, USA Department of Dermatology, Harvard Medical School, Boston, Massachusetts, USA Department of Infectious Diseases, First Affiliated College and Hospital, Guangxi Medical University, Nanning, China.
authors.forename: Liyi
authors.initials: L
authors.lastname: Huang
authors.affiliation: Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, Massachusetts, USA Department of Molecular Medicine, University of Siena, Siena, Italy.
authors.forename: Giacomo
authors.initials: G
authors.lastname: Landi
authors.affiliation: Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, Massachusetts, USA Department of Dermatology, Harvard Medical School, Boston, Massachusetts, USA Department of Dermatology, Dermatooncology and Venerology, Semmelweis University School of Medicine, Budapest, Hungary.
authors.forename: Pinar
authors.initials: P
authors.lastname: Avci
authors.affiliation: Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, Massachusetts, USA Department of Dermatology, Harvard Medical School, Boston, Massachusetts, USA Center for Lasers and Applications, Nuclear and Energy Research Institute, Sao Paulo, Brazil.
authors.forename: Andrea
authors.initials: A
authors.lastname: Rodas
authors.affiliation: Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, Massachusetts, USA Department of Dermatology, Harvard Medical School, Boston, Massachusetts, USA Harvard-MIT Division of Health Sciences and Technology, Cambridge, Massachusetts, USA hamblin@helix.mgh.harvard.edu.
authors.forename: Michael R
authors.identifier: http://orcid.org/0000-0001-6431-4605
authors.initials: MR
authors.lastname: Hamblin
mesh_terms: D008027:Light; D008751:Methylene Blue / Q000737:chemistry*; D017319:Photosensitizing Agents / Q000737:chemistry*; D011193:Potassium Iodide / Q000737:chemistry*; D017382:Reactive Oxygen Species / Q000378:metabolism; D013211:Staphylococcus aureus / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects
chemical_list: D017319:Photosensitizing Agents; D017382:Reactive Oxygen Species; D011193:Potassium Iodide; D008751:Methylene Blue