Antibacterial Activity of Blue Light against Nosocomial Wound Pathogens Growing Planktonically and as Mature Biofilms

<jats:title>ABSTRACT</jats:title><jats:p>The blue wavelengths within the visible light spectrum are intrinisically antimicrobial and can photodynamically inactivate the cells of a wide spectrum of bacteria (Gram positive and negative) and fungi. Furthermore, blue light is equally effective against both drug-sensitive and -resistant members of target species and is less detrimental to mammalian cells than is UV radiation. Blue light is currently used for treating acnes vulgaris and<jats:named-content content-type="genus-species">Helicobacter pylori</jats:named-content>infections; the utility for decontamination and treatment of wound infections is in its infancy. Furthermore, limited studies have been performed on bacterial biofilms, the key growth mode of bacteria involved in clinical infections. Here we report the findings of a multicenter<jats:italic>in vitro</jats:italic>study performed to assess the antimicrobial activity of 400-nm blue light against bacteria in both planktonic and biofilm growth modes. Blue light was tested against a panel of 34 bacterial isolates (clinical and type strains) comprising<jats:named-content content-type="genus-species">Acinetobacter baumannii</jats:named-content>,<jats:named-content content-type="genus-species">Enterobacter cloacae</jats:named-content>,<jats:named-content content-type="genus-species">Stenotrophomonas maltophilia</jats:named-content>,<jats:named-content content-type="genus-species">Pseudomonas aeruginosa</jats:named-content>,<jats:named-content content-type="genus-species">Escherichia coli</jats:named-content>,<jats:named-content content-type="genus-species">Staphylococcus aureus</jats:named-content>,<jats:named-content content-type="genus-species">Enterococcus faecium</jats:named-content>,<jats:named-content content-type="genus-species">Klebsiella pneumoniae</jats:named-content>, and<jats:named-content content-type="genus-species">Elizabethkingia meningoseptica</jats:named-content>. All planktonic-phase bacteria were susceptible to blue light treatment, with the majority (71%) demonstrating a ≥5-log<jats:sub>10</jats:sub>decrease in viability after 15 to 30 min of exposure (54 J/cm<jats:sup>2</jats:sup>to 108 J/cm<jats:sup>2</jats:sup>). Bacterial biofilms were also highly susceptible to blue light, with significant reduction in seeding observed for all isolates at all levels of exposure. These results warrant further investigation of blue light as a novel decontamination strategy for the nosocomial environment, as well as additional wider decontamination applications.</jats:p><jats:p><jats:bold>IMPORTANCE</jats:bold>Blue light shows great promise as a novel decontamination strategy for the nosocomial environment, as well as additional wider decontamination applications (e.g., wound closure during surgery). This warrants further investigation.</jats:p>