The Research and Articles below are provided by BlueGuard LEDS, LLC. For information on the benefits of BlueGuard® antimicrobial /antibacterial products, please contact Pat McCray, Chairman & Founder at 904 401 - 1011 , pmccray.bgleds@gmail.com Research Index 1. Blue Light Kills MRSA Superbug 2. Blue Light Treats MRSA Infections 3. Blue Light Kills MRSA (without UV) 4. Blue Light Phototherapy Kills Antibiotic - Resistant Bacteria 5. Blue Lig ht eliminates community - acquired methicillin - resistant Staphylococcus aureus in infected mouse skin abrasions. 6. Blue 470 - nm light kills methicillin - resistant Staphylococcus aureus (MRSA) in vitro. 7. Blue Light Therapy Kills MRSA 8. 405nm Light Technology for Ina ctivation of Pathogens and its Potential for Environmental Disinfection and Infection Control 9. Different photodynamic effects of blue light with and without riboflavin on methicillin - resistant Staphylococcus aureus (MRSA) and human keratin - bytes in vitro 10. Li ght Photobiomodulation Blue Light Kills MRSA Superbug Recently, important studies have been consistently showing that two of the most common strains of MRSA can be virtually eliminated through simple exposure to blue light Though fewer than 5 percent of MRSA strains can be killed by penicillin and 40 to 50 percent of MRSA strains have become resistant to antibiotics, they appear to have no resistance to blue light , which is free of UV radiation. Since blue light kills harmful bacterial naturall y, safely and without dangerous side effects , blue light therapy has already received FDA approval for the treatment of periodontal disease and acne A Blue Light MRSA Study Explained In this study , an average of 90.4% of both US - 300 (community acquired) and IS - 853 (hospital acquired) strains of MRSA were killed within m inutes of exposure to simple blue light. This should be all over the national and world news. Why isn’t it? Maybe people don’t know what it means. Here is what the study said: “These significant levels of photo - destruction at low dosages indicate that irradiation with 470nm LED light energy may be a practical, inexpensive alternative to treatment with pharmacological agents, particularly in cases involving cutaneous and subcutan eous MRSA infections that are susceptible to non - invasive types of radiation.” Here’s what it means: “significant levels of photo - destruction” – an average of 90.4% of MRSA bacteria experienced ‘death by light.’ “low dosages” – simple light was used, not l ow - level laser light, not laser light, and it only took a few minutes of exposure to kill significant amounts of bacteria – 30% dying after just 100 seconds of exposure. “irradiation” – Light shining on something. Light of any color from any source is actu ally powerful electromagnetic energy, or radiation, and so light of any color can also be called “radiation.” When you shine any light on something, its being irradiated. It’s not as dangerous or expensive as it sounds. These two girls survive by daily high doses of 405 - 485nm (blue) ”irradiation.” “470nm” – blue. That’s it. Click here for a more detailed explanation. A previous study was done with similar results with 405nm light, which is visible violet light, very close to UVA on the electromagnetic spectrum. The actual span of the light used in this case was 455 - 485nm.Since 405nm also worked, it stands to reason that all wavelengths from 405 through 485 would have the same effect. That is blue light, period. “LED light energy” – as touched on above, all light is energy, the source does not matter. In this ca se, SLDs (superluminous diodes) were used, which are just the latest advancement in LED lighting – nothing special. LEDs are commonly used in medical research because they largely eliminate the factor of heat. Any blue light source that peaked around 470 nm should have produced the same results. “practical, inexpensive alternative to treatment with pharmacological agents” – easier and cheaper than drugs. They did not mention it’s also 100% natural, having no adverse side effects reported, non - invasive, pa inless, simply administered at home... and it’s worth double mention – easy to obtain, easy to use, and very cheap. “cases involving cutaneous and subcutaneous MRSA infections that are susceptible to non - invasive types of radiation.” – cases of MRSA infectio ns on and just beneath the surface of the skin, where the light is able to penetrate naturally. Since simple blue light killed an average of 90% of MRSA bacteria in the lab, it may turn out to be a practical, inexpensive alternative to treatment with drug s for cases of MRSA infections of or just under the skin in humans. Further Research Supporting Blue Light Therapy for MRSA Treatment Now What? I would not wait for further studies, FDA approval, or fancy marketing before I tried this out on myself or a lo ved one battling a MRSA infection on or just under the skin. The antibacterial properties of blue light have been known for quite some time – in fact the FDA approved blue light to kill acne bacteria in 2002. There are many “acne treatment lights” already available and in use today containing the same wavelengths used to kill MRSA, it would be very simple for them to be re - purposed immediately in the case of a MRSA infection of the skin not responding to antibiotics. It would also be good to have one of the se lights around to disinfect everyday cuts, burns and bites as a matter of MRSA prevention At the time of this writing, to my knowledge, blue light therapy has not yet been FDA approved for MRSA treatment. As a result, you won’t find in - home devices mar keted for MRSA treatment yet. However, an internet search for an “acne light” will turn up many lights that will work for MRSA treatment in all price ranges Here’s some tips for choosing one: 1. Choose blue light only , not red and blue light combined. Blue light is what kills bacteria, and that is what you need right now. Red light is for healing skin – you can take care of that later. You want the full power output of the light to be blue. 2. You’re going to find two different styles of lights: small, portable, hand - held lights, and large, table - top lights, specifically designed for treating your face. Unless your infection is actually on your face, buy a hand - held light so you can conveniently and fully cover any area. Understanding Blue Light W avelengths What makes one blue light more effective than another against MRSA is it’s wavelength. Wavelength is the scientific measurement that, when translated into practical terms, means “color.” The studies referenced in this article prove that blue li ght with peak wavelengths of 405 nm and 470 nm are effective against MRSA bacteria. What are the differences, and how do they affect your treatment? THE DIFFERENCES BETWEEN 405 AND 470 NM BLUE LIGHT LED Peak Wavelength: 405 nm 470 nm Visible Color: Violet Blue Wavelength / Energy: Shorter wavelength / higher energy Slightly longer wavelength, slightly less energy THE DIFFERENCES BETWEEN 405 AND 470 NM BLUE LIGHT Effectiveness: More effective Less effective Penetration of Skin: Surface only Penetrates the skin slightly deeper Treatment Time: Shorter Longer UV Content: Likely almost 1/2 UVA content Likely zero UVA content Blue Light Treats MRSA Infections submitted by: admin on 01/09/2014 An article published in November of 2013 in the journal, Photomedicine and Laser Surgery , documented that using blue light therapy at both 405 and 470 nm was effective in vivo to treat skin infections in rats infected with MRSA. More than two billion people now carry some strain of staphlococcus aureus, and 53 million now carry MRSA ( methicillin resistant staph aureus), and this accounts for about 20,000 deaths in the US every year. Overall, there are about 100,000 deaths annually in the US from antibiotic resistant microbes such as C. diff, klebsiella, E. coli, etc. MRSA accounts for 44% of all hospital associated infections in the US. Approximately 5% of people who go into the hospital without an infection come out of the hospital with a hospital acquired infection. There are now at least four alternative approaches to treat antibiot ic resistant infections and they include: hyperbaric oxygen, photodynamic therapy, antibacterial clays , and blue light phototherapy. Each of these modalities are briefly reviewed. Blue Light Kills MRSA Blue Light -- Without UV -- Kills Drug - Resistant Staph Superbug By Daniel J. DeNoon WebMD Health News Reviewed by Louise Chang, MD WebMD News Archive Feb. 4, 2009 -- Blue light -- not including dangerous UV frequencies -- kills MRSA , the multidrug - resistant staph superbug. The finding comes from Chukuka S. Enwemeka, PhD, and colleagues at New York Institute of Technology. Their study was funded by Dynatronics Corp., which makes the blue - light device used in the study. In earlier studies, Enwemeka's team found that MRSA died when exposed to blue light that included part of the ultraviolet (UV) spectrum. Even though the total UV dose was less than that of a few minutes of sunlight, it would be safer not to expose humans to any more UV light than necessary. So the researchers used a LED device that emits blue light not in the UV spectrum, and found it worked nearly as well. "Irradiation with [blue] light energy may be a practical, inexpensive alternative to treatment with pharmacologic agents, particularly in cases involving cutaneous and subcutaneous MRSA infections," Enwemeka and colleagues conclude. The researchers tested two MRSA strains: one typical of the strains that bedevil hospitals, and one typical of the strains found in the community. Both strains were susceptible to the blue light. Relatively low doses of blue light -- about 100 seconds' worth -- killed off about 30% of MRSA in laboratory cultures. Longer doses were more effective, although with diminishing returns. It took about 10 times longer exposure to kill off 80% of the MRSA in culture dishes. Exactly how blue light kills MRSA, or whether the bacteria can be come blue - light resistant, isn't known. The study will appear in the April 2009 issue of Photomedicine and Laser Surgery View Article Sources © 2009 WebMD, LLC. All rights reserved. Blue Light Phototherapy Kills Antibiotic - Resistant Bacteria, According to New Studies December 16, 2013 0 Comments Posted in News , Germicidal Light , Research Blue light has proven to have powerful bacteria - killing ability in the labo ratory. The potent antibacterial effects of irradiation using light in the blue spectra have now also been demonstrated in human and animal tissues. A series of groundbreaking articles that provide compelling evidence of this effect are published in Photom edicine and Laser Surgery, a peer - reviewed journal published by Mary Ann Liebert, Inc., publishers. The articles are available on the Photomedicine and Laser Surgery website. "Bacterial resistance to drugs poses a major healthcare problem," says co - editor in c hief Chukuka S. Enwemeka, PhD, dean of the College of Health Sciences at the University of Wisconsin - Milwaukee, in the accompanying editorial, "Antimicrobial Blue Light: An Emerging Alternative to Antibiotics," citing the growing number of deadly outbr eaks worldwide of methicillin - resistant Staphylococcus aureus (MRSA). The articles in this issue of Photomedicine and Laser Surgery provide evidence that "blue light in the range of 405 - 470 nm wavelength is bactericidal and has the potential to help stem t he ongoing pandemic of MRSA and other bacterial infections." In the article, "Effects of Photodynamic Therapy on Gram - Positive and Gram - Negative Bacterial Biofilms by Bioluminescence Imaging and Scanning Electron Microscopic Analysis," Aguinaldo S. Garcez, PhD and coauthors show that photodynamic therapy and methylene blue delivered directly into the root canal of a human tooth infected with a bacterial biofilm was able to destroy both Gram - positive and Gram - negative bacteria, disrupt the biofilms, and redu ce the number of bacteria adhering to the tooth. Raymond J. Lanzafame, MD, MBA, and colleagues demonstrated significantly greater bacterial reduction in the treatment of pressure ulcers in mice using a combination of photoactivated collagen - embedded compounds plus 455 nm diode laser irradiation compared to irradiation alone or no treatment. The antibacterial effect of the combined therapy increased with successive treatments, report the authors in the article "Preliminary Assessment of Photoactivated Antimicrobial Collagen on Bioburden in a Murine Pressure Ulcer Model." In the article "Wavelength and Bacterial Density Influence the Bactericidal Effect of Blue Light on Methicillin - Resistant Staphylococcus aureus (MRSA)," Violet Bumah, PhD, and coauthors compared the bacteria - killing power of 405 nm versus 470 nm light on colonies of resistant Staph aureus and how the density of the bacterial colonies could limit light penetration and the bactericidal effects of treatment. Source: Mary A nn Liebert, Inc. Blue light eliminates community - acquired methicillin - resistant Staphylococcus aureus in infected mouse skin abrasions. Dai T 1 , Gupta A , Huang YY , Sherwood ME , Murray CK , Vrahas MS , Kielian T , Hamblin MR Author information Abstract BACKGROUND AND OBJECTIVE: Bacterial skin and soft tissue infections (SSTI) affect millions of individuals annually in the United States. Treatment of SSTI has been significantly complicated by the increasing emergence of community - acquired methicillin - resistant Staphylococcus aureus (CA - MRSA) strains. The objective of this study was to demonstrate the efficacy of blue light ( 415 ± 10 nm) therapy for eliminating CA - MRSA infections in skin abrasions of mice. METHODS: The susceptibilities of a CA - MRSA strain (USA300LAC) and human keratinocytes (HaCaT) to blue light inactivation were compared by in vitro culture studies. A mouse m odel of skin abrasion infection was developed using bioluminescent USA300LAC::lux. Blue light was delivered to the infected mouse skin abrasions at 30 min (acute) and 24 h (established) after the bacterial inoculation. Bioluminescence imaging was used to m onitor in real time the extent of infection in mice. RESULTS: USA300LAC was much more susceptible to blue light inactivation than HaCaT cells (p=0.038). Approximately 4.75 - log10 bacterial inactivation was achieved after 170 J/cm(2) blue light had been del ivered, but only 0.29 log10 loss of viability in HaCaT cells was observed. Transmission electron microscopy imaging of USA300LAC cells exposed to blue light exhibited disruption of the cytoplasmic content, disruption of cell walls, and cell debris. In vivo studies showed that blue light rapidly reduced the bacterial burden in both acute and established CA - MRSA infections. More than 2 - log10 reduction of bacterial luminescence in the mouse skin abrasions was achieved when 41.4 (day 0) and 108 J/cm(2) (day 1) blue light had been delivered. Bacterial regrowth was observed in the mouse wounds at 24 h after the blue light therapy. CONCLUSIONS: There exists a therapeutic window of blue light for bacterial infections where bacteria are selectively inactivated by blu e light while host tissue cells are preserved. Blue light therapy has the potential to rapidly reduce the bacterial load in SSTI. PMID: Blue 470 - nm light kills methicillin - resistant Staphylococcus aureus (MRSA) in vitro. Enwemeka CS 1 , Williams D , Enwemeka SK , Hollosi S , Yens D Author information Abstract BACKGROUND DATA: 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. OBJECTIVE: 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. MATERIALS AND METHODS: 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 sp ecimens 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. RESULTS: 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. CONCLUSION: 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. Blue Light Therapy Kills MRSA One of the latest developments in fighting MRSA bacteria colonizing a person’s skin is the use of “blue light” therapy devices. Usually used for treating skin conditions, particularly those affecting the face, blue light therapy devices have been found to eradicate MRSA. How does blue light therapy kill MRSA? Recent studies have shown that all bacteria, including MRSA are highly sensitive (i.e. can be killed by) light that is between 405 - nm and 470 - nm. Light in this spectrum is blue in color, hence the name. The other good news is that the bacteria are unable to develop a resistance to this form of treatment, so the blue light just keeps on killing! Where can I get blue light therapy to treat my MRSA infection? You have a few options here. You could contact a medical center that offers blue light therapy for their patients such as a beauty therapy clinic and ask them if they are prepared to treat your MRSA infection with one of their devices. Bear in mind though tha t due to the fact that MRSA is highly contagious they may well refuse. If that happens don’t despair because there is another option...blue light therapy devices can be found online fairly easily on places such as Amazon, the world’s largest online marketpla ce. Just do a search for Blue Light Therapy Device or just click here to get the Project E Beauty LED 3 Colors Photo - rejuvenation Kit Facial Beauty Care Massager Be aware though that many of these devices are very expensive (i.e. hundreds of dollars) because the sellers are playing the MRSA card, and as such have “inflated” their prices. The third option is that you could ask an electrician or lighting specialist to locate a suitable bulb for you. Any LED blue light bulb that is between 405nm and 470nm with an energy density of 55 J/cm2 should do the trick. In several laboratory tests, a bulb that has an energy density as low as 3 J/cm2 was found to be still effective at killing MRSA. Is it safe? Blue light therapy devices that run between 405nm and 470nm are extremely safe as they are not in the UV spectrum. There are no known side effects of blue light therapy. Do I recommend blue light therapy as a treatm ent for MRSA? Unfortunately, by the time I found out about “blue light treatment” I had already recovered from MRSA so I never got the opportunity to try it for myself. In saying that though, I am aware of it working for several other people I know. I cert ainly believe that if you can get some blue light therapy treatment, you should do so. A quick reminder... Don’t forget, Staph is extremely common and most, if not all people have it on their skin. It only becomes a problem when your immunity is lowered to the point where your body can longer keep it at bay. This is when you get infected and get boils or something similar. So...ultimately your best defense is to strengthen your immune system, but this takes time. So...while this is happening, anything you can do to reduce the amount of staph on your body will help as it will reduce the risk of re - infection due to the number of bacteria being reduced. This in turn means that your body can expend more of its energy actually healing itself than fighting the infect ion. 405nm Light Technology for Inactivation of Pathogens and its Potential for Environmental Disinfection and Infection Control Article in the Journal of Hospital Infection September 2015 Authors: M. Maclean University of Strathclyde J.G. Anderson University of Strathclyde Karen McKenzie University of Strathclyde Background Although the germicidal properties of ultraviolet (UV) light have long been known, it is only comparatively recently that the antimicrobial properties of visible viole t – blue 405 nm light have been discovered and used for environmental disinfection and infection control applications. Aim To review the antimicrobial properties of 405 nm light and to describe its application as an environmental decontamination technology w ith particular reference to disinfection of the hospital environment. Methods Extensive literature searches for relevant scientific papers and reports. Findings A large body of scientific evidence is now available that provides underpinning knowledge of th e 405 nm light - induced photodynamic inactivation process involved in the destruction of a wide range of prokaryotic and eukaryotic microbial species, including resistant forms such as bacterial and fungal spores. For practical application, a high - intensity narrow - spectrum light environmental disinfection system (HINS - light EDS) has been developed and tested in hospital isolation rooms. The trial results have demonstrated that this 405 nm light system can provide continuous disinfection of air and exposed su rfaces in occupied areas of the hospital, thereby substantially enhancing standard cleaning and infection control procedures. Conclusion Violet – blue light, particularly 405 nm light, has significant antimicrobial properties against a wide range of bacteria l and fungal pathogens and, although germicidal efficacy is lower than UV light, this limitation is offset by its facility for safe, continuous use in occupied environments. Promising results on disinfection efficacy have been obtained in hospital trials b ut the full impact of this technology on reduction of healthcare - associated infection has yet to be determined. Although less germicidal than ultraviolet (UV) light, 405 nm light has broad - spectrum antimicrobial action against Gram positive and negative b acteria, bacterial biofilms, endospores, yeasts, fungi and in some circumstances viruses [5][6][7][8][9][10][11]. When used at appropriate irradiances, these wavelengths of visible light can also exert antimicrobial effects whilst being nondetrimental to m ammalian cells [12][13][14], giving it operational advantages over UV - light for applications such as continuous decontamination of occupied environments [15][16][17][18] and wound decontamination [12]. Additionally, it has recently been reported that 405 n m light can also have a synergistic antimicrobial effect with common chlorinated disinfectants, providing further support for its beneficial use for environmental decontamination [19]. ... ... Although 405 nm light has extensive antimicrobial action and sa fety advantages, little is known about the potential for the development of bacterial resistance or tolerance to violet - blue 405 nm light inactivation. It is hypothesised that tolerance is unlikely due to the mechanism of inactivation [13,17,20]. Similar t o that of photodynamic inactivation (PDI), which makes use of an additional photosensitizer, the mechanism of inactivation is thought to be non - selective, as the ROS and 1 O 2 produced cause unspecific damage to a wide spectrum of targets within bacterial cells [13,17,20,21]. ... ... It is hypothesised that tolerance is unlikely due to the mechanism of inactivation [13,17,20]. Similar to that of photodynamic inactivation (PDI), which makes use of an additional photosensitizer, the mechanism of inactivation is thought to be non - selective, as the ROS and 1 O 2 produced cause unspecific damage to a wide spectrum of targets within bacterial cells [13,17,20,21]. Nevertheless there is little evidence available to support this hypothesis. ... 7,[44][45] More recen tly, there have been several studies evaluating a visible - light CED system that provides continuous environmental disinfection in an occupied setting. [46][47][48] The visible - light CED system inactivates a wide range of bacterial pathogens in the air and on surfaces using a narrow bandwidth of high - intensity visible light with peak output at 405 § 5 nm. Visible light in this spectrum has been shown to incite bacterial cell death via photo - excitation of porphyrins within the bacteria. ... ... Visible light in this spectrum has been shown to incite bacterial cell death via photo - excitation of porphyrins within the bacteria. 46,[49][50][51][52][53][54][55] Clinical and laboratory studies have shown significant reductions in bacterial contamination of various h ealth care settings including isolation rooms, a burn unit, and an intensive care unit, with use of the visible - light CED system. [46][47][48] Although light in this wavelength range is less germicidal than UV light, these systems have the notable benefit of being safe for use in occupied spaces, while providing the necessary illumination required for surgery. ... ... 46,[49][50][51][52][53][54][55] Clinical and laboratory studies have shown significant reductions in bacterial contamination of various healt h care settings including isolation rooms, a burn unit, and an intensive care unit, with use of the visible - light CED system. [46][47][48] Although light in this wavelength range is less germicidal than UV light, these systems have the notable benefit of b eing safe for use in occupied spaces, while providing the necessary illumination required for surgery. Additionally, because they can be used continuously, they can provide disinfection throughout the day, actively addressing organisms shed in the air and on surfaces by OR staff during cases and between manual cleanings. ... However, recently, with the introduction of new technologies, researches evaluating the antimicrobial effect of light emitting diode (LED) in visible light spectrum and ultraviolet lig ht spectrum have emerged (Maclean et al., 2014). A LED is a compact electronic device that emits light within a monochromatic wavelength spectrum, when electric current passes through it. ... ... Salmonella entericae Enterococcus faecalis are two studied bacteria with greater resistance to inactivation by exposure to visible light, requiring long periods of exposure. The reasons for these different susceptibilities are still indeterminate, but analysis indicates that grampositive bacteria tend to be more susceptible to inactivation than gram - negative (Maclean et al., 2009;2014;Murdoch et al., 2012). Therefore, there will be cells that cannot be injured and can multiply in the time interval. ... ... However, the fact th at this wavelength lies within the visible light range and does not require the necessary protections for UV light, it can be continuously for treatment of water, food as well as surfaces. It can be safely used in the presence of people in the same enclosu re, it is easy to operate, and it has high penetration power in water, plastics and glass (Maclean et al., 2014). ... The blue wavelengths within the visible light spectrum (especially wavelengths between 400 nm to 470 nm) are intrinsically antimicrobial and do not require additional exogenous photosensitizers to exert an antimicrobial effect [12]. Photodynamic inactivation of bacterial cells occurs due to photo - excitation of intracellular porphyrins [13] by the blue light (BL), leading to energy transfer and the production of highly cytotoxic reactive oxygen species (ROS); primarily singlet oxygen ( 1 O 2 ) [12,[14][15][16]. Although less germicidal compared to ultra - violet light [13], pathogens can be selectively inactivated whilst preserving human cells and consequently BL is considered much less detrimental to mammalian cells [17,18]. ... ... Photodynamic inactivation of bacterial cells occurs due to photo - excitation of intracellular porphyrins [13] by the blue light (BL), leading to energy transfer and the production of highly cytotoxic reactive oxygen species (ROS); primarily singlet oxygen ( 1 O 2 ) [12,[14][15][16]. Although less germicidal compared to ultra - violet light [13], pathogens can be selectively inactivated whilst preserving human cells and consequently BL is considered much less detrimental to mammalian cells [17,18]. ... ... BL has been shown to exhibit a broad spectrum of antimicrobial effect against bacteria and fungi [19][20][21], and has been investigated as a new disinfection technolo gy termed the HINS - light environmental decontamination system (HINS - EDS) [13,[22][23][24]. The HINS - EDS is a type of ceiling - mounted lightbulb which delivers low - irradiance 405 nm light continuously and is suitable for use in patient occupied settings. .. Light - emitting diodes (LEDs) demonstrate therapeutic effects for a range of biomedical 24 applications including photodisinfection. Specific wavelength bands (centred at 405nm) are 25 reported to be the most antimicrobial, however there remains no consens us on most effective 26 irradiation parameters for optimal photodisinfection. The aim of this study was to assess 27 decontamination efficiency by direct photodisinfection of monomicrobial biofilms using single 28 (SWA), and multi wavelength (MWA) violet - b lue light (VBL) arrays. ... ... Consequently, without the need for exogenous chemicals, and the reduced photon energy of 94 longer wavelengths, direct photodisinfection using VBL may allow for development of more Recently light emitting devices (405 nm) ha ve been incorporated into a new disinfection 99 technology termed the 'high intensity narrow spectrum light environmental decontamination 100 system' (HINS - EDS) [21][22][23][24]. The HINS - EDS is a ceiling - mounted LED array which delivers low - 101 6 irradian ce 405nm light (irradiance of 0.1 - 0.5 mW/cm 2 ) continuously to decontaminate surfaces 102 in hospital operating theatres [16,25] . Evaluation studies showed that there was a statistically 103 significant 91% reduction in numbers of culturable Staphylococc i spp. ... ... Violet - blue light, particularly that of 405 nm wavelength, shows significant antimicrobial action against a wide range of microorganisms and, although its germicidal efficiency is lower than ultraviolet (UV) light, this drawback is counterb alanced by its convenience for safe and continuous use in working environments ( Maclean et al., 2014). The photoinactivation process induced by 405 nm light exposure implies a multi - targeted biocide effect due to the production of ROS, a lethal mechanism that does not lead to microbial hardiness ( Maclean et al., 2014). Interestingly, a review compiling data of more than 50 published studies on inactivation of about 40 different bacterial species caused by visible light (from 380 to 780 nm) and endogenous PS, revealed that under aerobic conditions almost all bacteria, including both Gram - positive, as well as Gram - negative, except spores are reduced by at least 3 logs following receiving a dose of about 500 J/cm 2 of 405 nm irradiation ( Hessling et al., 201 7). ... • Original Article • Open Access • Published: 30 March 2019 Different photodynamic effects of blue light with and without riboflavin on methicillin - resistant Staphylococcus aureus (MRSA) and human keratinocytes in vitro • Karim Makdoumi , • Marie Hedin & • Anders Bäckman Lasers in Medical Science volume 34 , pages 1799 – 1805(2019) Cite this article • 1080 Accesses • 1 Citations • 0 Altmetric • Metrics details Abstract Methicillin - resistant Staphylococcus aureus (MRSA) is an important cause of infections in humans. Photodynamic therapy using blue light (450 nm) co uld possibly be used to reduce MRSA on different human tissue surfaces without killing the human cells. It could be less harmful than 300 – 400 nm light or common disinfectants. We applied blue light ± riboflavin (RF) to MRSA and keratinocytes, in an in vitr o liquid layer model, and compared the effect to elimination using common disinfection fluids. MRSA dilutions (8 × 10 5 /mL) in wells were exposed to blue light (450 nm) ± RF at four separate doses (15, 30, 56, and 84 J/cm 2 ). Treated samples were cultivated on blood agar plates and the colony forming units (CFU) determined. Adherent human cells were cultivated (1 × 10 4 /mL) and treated in the same way. The cell activity was then measured by Cell Titer Blue assay after 24 - and 48 - h growth. The tested disinfectants were chlorhexidine and hydrogen peroxide. Blue light alone (84 J/cm 2 ) eliminated 70% of MRSA. This dose and riboflavin eradicated 99 – 100% of MRSA. Keratinocytes were not affected by blue light alone at any dose. A dose of 30 J/cm 2 in ribofla vin solution inactivated keratinocytes completely. Disinfectants inactivated all cells. Blue light alone at 450 nm can eliminate MRSA without inactivation of human keratinocytes. Hence, a high dose of blue light could perhaps be used to treat bacterial inf ections without loss of human skin cells. Photodynamic therapy using riboflavin and blue light should be explored further as it may perhaps be possible to exploit in treatment of skin diseases associated with keratinocyte hyperproliferation. Introduction M ethicillin - resistant Staphylococcus aureus (MRSA) is one of the most important bacterial pathogens associated with morbidity and mortality [ 1 , 2 ]. The development of new pharmacological agents is a complicated and slow process, with antibiotic resistance emerging as an increasing problem. Several approaches have been proposed to maintain the e fficacy of currently available antimicrobials. These include educational efforts to reduce unnecessary prescription as well as infrastructural strategies to improve sanitation and limit spread of drug - resistant microorganisms. Furthermore, vaccines, probio tics, and more non - specific antimicrobials have been suggested as possible therapeutic strategies against infections [ 3 , 4 , 5 ]. Photodynamic therapy (PDT) or Photodynamic Ant imicrobial Chemotherapy (PACT) is a mode of treatment which has been considered for local infections, and evaluated through in vitro and in vivo experiments [ 6 , 7 ]. Excitation of a photosensitizer by light il lumination generates reactive oxygen species (ROS) which results in pathogen elimination [ 8 , 9 , 10 ]. However, blue light (400 – 470 nm) can eliminate both Gram - positive and Gram - negative bacteria without chromophores [ 8 , 11 ] and is considered to be less harmful to human cells compared to UV irradiation [ 8 , 12 ]. It is believed that endogenous intracellular porphyrins are excited by blue light irradiation which functions as photosensitizers [ 13 , 14 ]. Wavelengths between 402 and 420 nm are seemingly more effective than longer wavelength of blue light (455 and 470 nm) although the longer wavelengths may have some advantages in elimination of dense bacterial cultures with high colony forming unit (CFU) counts [ 15 , 16 , 17 , 18 , 19 ]. Blue light in the lower wavelength spectrum (400 – 425 nm) can be utilized to trea t acne vulgaris with few side - effects reported [ 20 , 21 , 22 ]. Riboflavin (RF) (vitamin B2) is a non - toxic photosensitizer that can be used together with UV irradiation of blood components in order to eliminate microorganisms [ 23 , 24 , 25 , 26 ]. Combined with ultraviolet light A, it is also clinically used in the treatment of corneal ectas ia, such as keratokonus and has been evaluated in management of recalcitrant corneal infections [ 27 ]. We have previously investigated eradication of MRSA in vitro, mediated by riboflavin photoactivated using ultraviolet light A (365 nm) [ 28 , 29 , 30 ] and blue light (412 nm and 450 nm) [ 31 ] in thin layers of fluid (0.4 – 1.76 mm). In these experiments, the elimination of blue light was augmented by the presence of riboflavin, and a relatively low dose was required to eliminate MRSA in a thin fluid - layer with the photosensitizer. In a thicker fluid - layer (1.17 mm), with higher number of bacteria, the effect (of 412 nm) was reduced (91% with riboflavin), which is con sistent with other publications [ 18 , 19 ] but the longer wavelength (450 nm) was not evaluated under these conditions. It is possible that light with wavelength 450 nm is advantageous compared to 412 nm and could cause less damage to human cells but still be useful for inactivation of microorganisms. A higher dose of 450 nm would likely be required to mediate an antimicrobial effect in a thicker fluid layer and the impact on human cells must also be evaluated if this method should be considered for any in vivo application. We therefore aimed to determine the effect of higher doses (≥ 30 J/cm 2 ) of blue light (450 nm) in a 1.2 mm fluid layer, with and wit hout riboflavin for eradicating MRSA. Similarly, exposure was done on human keratinocytes as an indicator of effects of these dosages on human epithelial cells. Material and methods Blue light source and exposure levels A prototype diode lamp (TERUMO.BCT, Lakewood, Colorado, USA) was used for irradiation, (Total Power Output = 7.14 W, peak wavelength = 450 nm) with three parallel light - emitting diodes (LedEngin, Inc., CA, USA) in a row spanning over 4.5 cm, without light collimation, inside a square illumin ation box. Calibration was conducted prior to the experiments, on six different representative locations inside the illumination chamber to control adequate exposure of all wells (308 UV - intensity meter, OAI, CA, USA, 436 nm detector 308 - 0002 - 11). The defi ned irradiance was a mean of these six measurements. Bacterial and keratinocyte suspensions were treated with four different doses of 450 nm as measured at the fluid level in the experiment. Dose 1, 15 J/cm 2 (irradiance = 25 mW/cm 2 , time = 10 min). Dose 2, 30 J/cm 2 (irradiance = 25 mW/cm 2 , time = 20 min. Dose 3, 56 J/cm 2 , (irradiance = 46.6 mW/cm 2 , time = 20 min). Dose 4, 84 J/cm 2 (irradiance = 46.6 mW/cm 2 , time = 30 min). The distance to the LED - lamps was 13 cm for the two lower dose s and 9 cm for the higher light exposure. The exposed area evaluated during illumination was 16.25 cm 2 MRSA reduction after light exposure Staphylococcus aureus resistant to methicillin and oxacillin (MRSA) (American Type Culture Collection (ATCC) no. 433 00), stored at − 80 °C and cultured at 37 °C, was obtained from colonies on blood agar plates. The bacteria were counted in a Bürker Chamber and diluted in sterile phosphate buffered saline (PBS) (no: 14190 - 094, Gibco by Life Technologies, Life Technologie s Corp., Paisley,UK) to approximately 4 × 10 6 CFU/mL. Further dilution was made using cell culture medium (RPMI, Gibco no: 11835 - 063) with and without addition of riboflavin (RF), final concentration in suspensions 0.01% (no. R7649 - 25G, SIGMA - Aldrich, Schn elldorf, Germany). The estimated CFU/mL concentration in solutions was 8 × 10 5 CFU/mL at the start of experiments. Bacterial mixtures were placed in specific wells ( n = 3) on cell culture plates (40 μL per well, 6.5 mm diameter, fluid thickness 1.2 mm) (Sa rstedt 96 well plate, no: 83.392