Blue 470-nm Light Kills Methicillin-Resistant Staphylococcus aureus (MRSA) in Vitro

School of Health Professions, Behavioral, and Life Sciences, New York Institute of Technology, Old Westbury, New York 11568-8000, USA.
Photomedicine and laser surgery (Impact Factor: 1.67). 04/2009; 27(2):221-6. DOI: 10.1089/pho.2008.2413
Source: PubMed


In a previous study, we showed that 405-nm light photo-destroys methicillin-resistant Staphylococcus aureus (MRSA). The 390-420 nm spectral width of the 405-nm superluminous diode (SLD) source may raise safety concerns in clinical practice, because of the trace of ultraviolet (UV) light within the spectrum.
Here we report the effect of a different wavelength of blue light, one that has no trace of UV, on two strains of MRSA--the US-300 strain of CA-MRSA and the IS-853 strain of HA-MRSA--in vitro.
We cultured and plated each strain, and then irradiated each plate with 0, 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 25, 30, 35, 40, 45, 50, 55, or 60 J/cm2 of energy a single time, using a 470-nm SLD phototherapy device. The irradiated specimens were then incubated at 35 degrees C for 24 h. Subsequently, digital images were made and quantified to obtain colony counts and the aggregate area occupied by bacteria.
Photo-irradiation produced a statistically significant dose-dependent reduction in both the number and the aggregate area of colonies formed by each strain (p < 0.001). The higher the dose the more bacteria were killed, but the effect was not linear, and was more impressive at lower doses than at higher doses. Nearly 30% of both strains was killed with as little as 3 J/cm2 of energy. As much as 90.4% of the US-300 and the IS-853 colonies, respectively, were killed with an energy density of 55 J/cm2. This same dose eradicated 91.7% and 94.8% of the aggregate area of the US-300 and the IS-853 strains, respectively.
At practical dose ranges, 470-nm blue light kills HA-MRSA and CA-MRSA in vitro, suggesting that a similar bactericidal effect may be attained in human cases of cutaneous and subcutaneous MRSA infections.

    • "Overall, our findings indicate that the viability of fibroblasts decreases progressively with increasing dose (i.e., fluence or energy density ) of 470 nm blue light, particularly at doses in the range of 110 J/cm 2 or higher, with significant modulation of mitochondrial metabolism, detectable alteration of lysosomal activity, cell membrane perturbation and observable alteration of cell morphology. In previous studies, we showed that irradiation with 405 nm or 470 nm blue light is antimicrobial to methicillin-resistant Staphylococcus aureus (MRSA), and that the extent of bacterial suppression increases with energy density (Bumah et al., 2013;Bumah, Masson-Meyers, Cashin, et al., 2015;Bumah, Masson-Meyers &amp; Enwemeka, 2015;Bumah, Masson-Meyers, Quirk, et al., 2015;Enwemeka, 2013;Enwemeka et al., 2008Enwemeka et al., , 2009Masson-Meyers et al., 2015). Our finding that doses in the range of 220 J/cm 2 are inimical to human fibroblasts, i.e., impair cell membrane integrity, disrupt lysosomal function and alter the metabolism of mitochondria , suggests that such high doses should be avoided in order to minimize damage to normal cells; even when bacterial suppression with blue light is a necessary goal. "
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    ABSTRACT: Introduction: Several tests are available for assessing the viability of cells; however, there is a dearth of studies comparing the results obtained with each test. We compared the capability of four viability assays (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT), neutral red, trypan blue and live/dead fluorescence), to detect potential toxicity in fibroblasts irradiated with 470 nm blue light. Methods: Cells were irradiated at 3, 55, 110 and 220 J/cm2, incubated for 24 h and viability assessed using each test. Results: MTT assay showed significant decreases in viability when cells were irradiated with 110 and 220 J/cm2 energy fluence (dose) (89% and 57% viable cells, respectively; p b 0.0001, compared to control); likewise the trypan blue assay showed 42% and 46% viable cells (p b 0.0001). Neutral red assay revealed significant decrease in viability when cells were irradiated with 220 J/cm2 (84% viable cells; p = 0.0008, compared to control). The live/dead fluorescence assay was less sensitive, evincing 91% and 95% viable cells after irradiation with 110 and 220 J/cm2 respectively. Discussion: (1) The four assays differed in their levels of sensitivity to cell viability. (2) The adverse effect of increasing doses seems to manifest as alteration of mitochondrial metabolism, followed by lysosomal dysfunction, membrane disruption and finally loss of cell membrane integrity. (3) Overall, irradiation with 3 J/cm2 or 55 J/cm2 did not adversely affect cell viability. Thus, doses below 110 J/cm2 appear safe.
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    • "It was also shown to be effective in acute, potentially lethal Pseudomonas aeruginosa burn infections in mice [129]. However the majority of the studies on the antimicrobial effect of blue light, especially for MRSA infections have been confined to in vitro studies [130] [131] [132]. As compared to UV, there is less concern about the mutagenic effects of blue light in mammalian cells as blue light is not absorbed by DNA. "
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    ABSTRACT: Methicillin-resistant Staphylococcus aureus (MRSA) has become the most important drug-resistant microbial pathogen in countries throughout the world. Morbidity and mortality due to MRSA infections continue to increase despite efforts to improve infection control measures and to develop new antibiotics. Therefore alternative antimicrobial strategies that do not give rise to development of resistance are urgently required. A group of therapeutic interventions have been developed in the field of photomedicine with the common theme that they rely on electromagnetic radiation with wavelengths between 200 and 1000 nm broadly called "light". These techniques all use simple absorption of photons by specific chromophores to deliver the killing blow to microbial cells while leaving the surrounding host mammalian cells relatively unharmed. Photodynamic inactivation uses dyes called photosensitizers (PS) that bind specifically to MRSA cells and not host cells, and generate reactive oxygen species and singlet oxygen upon illumination. Sophisticated molecular strategies to target the PS to MRSA cells have been designed. Ultraviolet C radiation can damage microbial DNA without unduly harming host DNA. Blue light can excite endogenous porphyrins and flavins in MRSA cells that are not present in host cells. Near-infrared lasers can interfere with microbial membrane potentials without raising the temperature of the tissue. Taken together these innovative approaches towards harnessing the power of light suggest that the ongoing threat of MRSA may eventually be defeated.
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    • "O efeito protetor da fototerapia sobre a incidência de mastite aqui verificado deve estar associado aos seus efeitos ativadores do metabolismo celular de ceratinócitos, fibroblastos e células inflamatórias (Young 1989, Houreld 2014) com consequente melhoria da imunidade local (Young 1989). Contudo experimentos recentes têm demonstrado que a fototerapia pode controlar a proliferação de microrganismos, mesmo bactérias altamente patogênicas, com o Staphylococcus aureus resistente à meticilina (Enwemeka et al. 2009). "
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