Methicillin Resistant Staph Aureus (MRSA)

Photomed Laser Surg. 2013 Nov;31(11):547-53. doi: 10.1089/pho.2012.3461. Epub 2013 Apr 27.

Wavelength and bacterial density influence the bactericidal effect of blue light on methicillin-resistant Staphylococcus aureus (MRSA).

Bumah VV1, Masson-Meyers DS, Cashin SE, Enwemeka CS.

Author information

  • 11 College of Health Sciences, University of Wisconsin-Milwaukee , Milwaukee, Wisconsin.



The purpose of this study was to investigate the effect of wavelength and methicillin-resistant Staphylococcus aureus (MRSA) density on the bactericidal effect of 405 and 470 nm light.


It is recognized that 405 and 470 nm light-emitting diode (LED) light kill MRSA in standard 5 × 10(6) colony-forming units (CFU)/mL cultures; however, the effect of bacterial density on the bactericidal effect of each wavelength is not known.


In three experiments, we cultured and plated US300 MRSA at four densities. Then, we irradiated each plate once with either wavelength at 0, 1, 3, 45, 50, 55, 60, and 220 J/cm(2).


Irradiation with either wavelength reduced bacterial colonies at each density (p<0.05). More bacteria were cleared as density increased; however, the proportion of colonies cleared, inversely decreased as density increased–the maximum being 100%, 96%, and 78% for 3 × 10(6), 5 × 10(6), and 7 × 10(6) CFU/mL cultures, respectively. Both wavelengths had similar effects on the sparser 3 × 10(6) and 5 × 10(6) CFU/mL cultures, but in the denser 7 × 10(6) CFU/mL culture, 405 nm light cleared more bacteria at each fluence (p<0.001). To determine the effect of beam penetration, denser 8 × 10(6) and 12 × 10(6) CFU/mL culture plates were irradiated either from the top, the bottom, or both directions. More colonies were eradicated from plates irradiated from top and bottom, than from plates irradiated from top or bottom at the same sum total fluences (p<0.001).


The bactericidal effect of LED blue light is limited more by light penetration of bacterial layers than by bacterial density per se.

Photomed Laser Surg. 2013 Nov;31(11):531-8. doi: 10.1089/pho.2012.3365. Epub 2013 Feb 13.

Blue light eliminates community-acquired methicillin-resistant Staphylococcus aureus in infected mouse skin abrasions.

Dai T1, Gupta A, Huang YY, Sherwood ME, Murray CK, Vrahas MS, Kielian T, Hamblin MR.

Author information

  • 11 Wellman Center for Photomedicine, Massachusetts General Hospital , Boston, Massachusetts.



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.


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 model 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 monitor in real time the extent of infection in mice.


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 delivered, 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.


There exists a therapeutic window of blue light for bacterial infections where bacteria are selectively inactivated by blue light while host tissue cells are preserved. Blue light therapy has the potential to rapidly reduce the bacterial load in SSTI.

An Bras Dermatol.  2013 Jan-Feb;88(1):50-5.

Low level laser therapy (AlGaInP) applied at 5J/cm2 reduces the proliferation of Staphylococcus aureus MRSA in infected wounds and intact skin of rats*.

s Silva DC, Plapler H, da Costa MM, e Silva SR, de Sa Mda C, e Silva BS


Faculdade Inspirar Petrolina, Petrolina, PE, Brazil.



Laser therapy is a low cost, non-invasive procedure with good healing results. Doubts exist as to whether laser therapy action on microorganisms can justify research aimed at investigating its possible effects on bacteria-infected wounds.


To assess the effect of low intensity laser on the rate of bacterial contamination in infected wounds in the skin of rats.


An experimental study using 56 male Wistar rats. The animals were randomly divided into eight groups of seven each. Those in the "infected" groups were infected by Staphylococcus aureus MRSA in the dorsal region. Red laser diode (AlGaInP) 658nm, 5J/cm2 was used to treat the animals in the "treated" groups in scan for 3 consecutive days. Samples were drawn before inoculating bacteria and following laser treatment. For statistical analysis we used the nonparametric Wilcoxon (paired data) method with a significance level of p <0.05.


The statistical analysis of median values showed that the groups submitted to laser treatment had low bacterial proliferation.


The laser (AlGaInP), with a dose of 5J/cm2 in both intact skin and in wounds of rats infected with Staphylococcus aureus MRSA, is shown to reduce bacterial proliferation.

Lasers Med Sci.  2012 Feb 23. [Epub ahead of print]

Phototoxic effect of curcumin on methicillin-resistant Staphylococcus aureus and L929 fibroblasts.

Ribeiro AP, Pavarina AC, Dovigo LN, Brunetti IL, Bagnato VS, Vergani CE, de Souza Costa CA.


Department of Dental Materials and Prosthodontics, Araraquara Dental School, UNESP-Univ. Estadual Paulista, Araraquara, SP, Brazil,


Photodynamic therapy has been investigated as an alternative method of killing pathogens in response to the multiantibiotic resistance problem. This study evaluated the photodynamic effect of curcumin on methicillin-resistant Staphylococcus aureus (MRSA) compared to susceptible S. aureus (MSSA) and L929 fibroblasts. Suspensions of MSSA and MRSA were treated with different concentrations of curcumin and exposed to light-emitting diode (LED). Serial dilutions were obtained from each sample, and colony counts were quantified. For fibroblasts, the cell viability subsequent to the curcumin-mediated photodynamic therapy was evaluated using the MTT assay and morphological changes were assessed by SEM analysis. Curcumin concentrations ranging from 5.0 to 20.0 M in combination with any tested LED fluences resulted in photokilling of MSSA. However, only the 20.0 M concentration in combination with highest fluence resulted in photokilling of MRSA. This combination also promoted an 80% reduction in fibroblast cell metabolism and morphological changes were present, indicating that cell membrane was the main target of this phototherapy. The combination of curcumin with LED light caused photokilling of both S. aureus strains and may represent an alternative treatment for eradicating MRSA, responsible for significantly higher morbidity and mortality and increased healthcare costs in institutions and hospitals.

Photomed Laser Surg. 2011 Jun;29(6):405-12. Epub 2011 Jan 10.

The use of 808-nm light therapy to treat experimental chronic osteomyelitis induced in rats by methicillin-resistant Staphylococcus aureus.

Kaya G, Kaya M, Gürsan N, Kireççi E, Güngörmü M, Balta H.


Department of Oral and Maxillofacial Surgery, Faculty of Dentistry, Atatürk University, Erzurum, Turkey.



In vivo and in vitro studies have reported that laser energy in differing wavelengths and irradiation regimes has a potential bactericidal effect on Staphylococcus aureus.


The purpose of this study was to investigate whether a light wavelength of 808 nm in varying doses has an effect on chronic osteomyelitis induced experimentally in the rat tibia.


Intramedullary cavities were surgically created in the left tibias of 39 adult Wistar albino rats. Five randomly selected subjects were injected with a sterile saline solution, and methicillin-resistant S. aureus (MRSA) was used to induce osteomyelitis in the remaining rats. After 3 weeks, rats with evidence of osteomyelitis were treated with debridement alone (n=7), with debridement plus laser irradiation to induce photoeradication (n=21), or were not treated at all [negative control, (n=6)]. Active irradiation was performed using an 808 nm, 100 mW continuous-wave diode laser with a beam spot size of 0.7854 cm(2) (irradiance=127.3 mW/cm(2)). Laser treatment commenced immediately after debridement surgery and was applied daily for 5 consecutive days. Irradiation lasted 60 secs (6 J at 7.64 J/cm(2): n=7), 120 secs (12 J at 15.29 J/cm(2): n=7), or 180 secs (18 J at 22.93 J/cm(2): n=7). Rats in the sham and negative control groups were killed 21 days post-induction surgery, and those in the treatment groups were killed after 42 days. Following killing, tibias were removed and analyzed histopathologically, radiographically, and microbiologically.


Histopathological analysis showed that infection levels had decreased by 37%, 67%, 81%, and 93% in the groups treated by debridement or by debridement plus 7.64, 15.29, and 22.93 J/cm(2) light therapy, respectively, compared to the negative control group. Osteomyelitis-induced rats had the highest bacteria count (5×10(5)). Bacterial counts fell to 1.6×10(4), 4.3×10(2), 5.5×10(1), and 3.3×10(0) in groups treated by debridement or by debridement plus 7.64, 15.29, and 22.93 J/cm(2) light therapy, respectively, compared to the negative control group.

Photomed Laser Surg. 2009 Apr;27(2):221-6.

Blue 470-nm light kills methicillin-resistant Staphylococcus aureus (MRSA) in vitro.

Enwemeka CS, Williams D, Enwemeka SK, Hollosi S, Yens D.

School of Health Professions, Behavioral, and Life Sciences, New York Institute of Technology, Old Westbury, New York 11568-8000,

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 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.

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.

Appl Environ Microbiol. 2009 Apr;75(7):1932-7. Epub 2009 Feb 6.

Inactivation of bacterial pathogens following exposure to light from a 405 nanometer light-emitting diode array.

Maclean M, MacGregor SJ, Anderson JG, Woolsey G.

The Robertson Trust Laboratory for Electronic Sterilisation Technologies, University of Strathclyde, 204 George Street, Glasgow, Scotland.

This study demonstrates the susceptibility of a variety of medically important bacteria to inactivation by 405-nm light from an array of light-emitting diodes (LEDs), without the application of exogenous photosensitizer molecules. Selected bacterial pathogens, all commonly associated with hospital-acquired infections, were exposed to the 405-nm LED array, and the results show that both gram-positive and gram-negative species were successfully inactivated, with the general trend showing gram-positive species to be more susceptible than gram-negative bacteria. Detailed investigation of the bactericidal effect of the blue-light treatment on Staphylococcus aureus suspensions, for a range of different population densities, demonstrated that 405-nm LED array illumination can cause complete inactivation at high population densities: inactivation levels corresponding to a 9-log(10) reduction were achieved. The results, which show the inactivation of a wide range of medically important bacteria including methicillin-resistant Staphylococcus aureus, demonstrate that, with further development, narrow-spectrum 405-nm visible-light illumination from an LED source has the potential to provide a novel decontamination method with a wide range of potential applications.

Photomed Laser Surg. 2006 Dec;24(6):684-8

In vitro bactericidal effects of 405-nm and 470-nm blue light.

Guffey JS, Wilborn J.

Physical Therapy Plus, Bauxite, Arkansas 72011, USA.

OBJECTIVE: The aim of this study was to determine the bactericidal effect of 405- and 470-nm light on two bacteria, Staphylococcus aureus and Pseudomonas aeruginosa, in vitro.

BACKGROUND DATA: It is well-known that UV light kills bacteria, but the bactericidal effects of UV may not be unique since recent studies indicate that blue light produces a somewhat similar effect. The effects of blue light seem varied depending on wavelength, dose and the nature of the bacteria, hence this study.

METHODS: Two common aerobes, Staphylococcus aureus and Pseudomonas aeruginosa, and anaerobic Propionibacterium acnes were tested. Each organism was treated with Super Luminous Diode probes with peak emission at 405 and 470 nm. Treatment was timed to yield 1, 3, 5, 10, and 15 Jcm2 doses. Colony counts were performed and compared to untreated controls.

RESULTS: The 405-nm light produced a dose dependent bactericidal effect on Pseudomonas aeruginosa and Staphylococcus aureus (p < .05), achieving as much as 95.1% and nearly 90% kill rate for each, respectively. The 470-nm light effectively killed Pseudomonas aeruginosa at all dose levels, but only killed Staphylococcus aureus at 10 and 15 J cm2. With this wavelength, as much as 96.5% and 62% reduction of Pseudomonas aeruginosa and Staphylococcus aureus was achieved, respectively. Neither of the two wavelengths proved bactericidal with anaerobic Propionibacterium acnes.

CONCLUSION: The results indicate that, in vitro, 405- and 470-nm blue light produce dose dependent bactericidal effects on Pseudomonas aeruginosa and Staphylococcus aureus but not Propionibacterium acnes.

Photomed Laser Surg. 2006 Dec;24(6):680-3.

Effects of combined 405-nm and 880-nm light on Staphylococcus aureus and Pseudomonas aeruginosa in vitro.

Guffey JS, Wilborn J.

Physical Therapy Plus, Bauxite, Arkansas 72011, USA.

OBJECTIVE: The aim of this study was to determine the effect of a combination of 405-nm blue light and 880-nm infrared light on Staphylococcus aureus and Pseudomonas aeruginosa in vitro.

BACKGROUND DATA: Reports indicate that certain wavelengths and treatment parameters of light promote the growth of bacteria, but our earlier study indicates that light at specific wavelengths and intensities are bactericidal for specific organisms (1).

METHODS: Two common aerobes, Staphylococcus aureus and Pseudomonas aeruginosa were tested because of their frequent isolation from skin infections and wounds. Each organism was treated simultaneously with a combination of 405-nm and 880-nm light emitted by a cluster of Super Luminous Diodes (SLDs). Doses of 1, 3, 5, 10, and 20 Jcm2 were used. Colony counts were performed and compared to untreated controls using Student t tests and one-way ANOVA with Tukey and Scheffe post hoc analyses.

RESULTS: The results revealed significant dose-dependent bactericidal effects of the combined blue and infrared light on Staphylococcus aureus (F 4,94 = 5.38, p = 0.001) and Pseudomonas aeruginosa (F 4,95 = 21.35, p < 0.001). With P. aeruginosa, the treatment reduced the number of bacteria colonies at all doses, achieving statistical significance at 1, 3, and 20 J cm2 doses and reducing bacterial colony by as much as 93.8%; the most effective dose being 20 J cm2. Irradiation of S. aureus resulted in statistically significant decreases in bacterial colonies at all dose levels; the most decrease, 72%, was also achieved with 20 Jcm2.

CONCLUSION: Appropriate doses of combined 405-nm and 880-nm phototherapy can kill Staphylococcus aureus and Pseudomonas aeruginosa in vitro, suggesting that a similar effect may be produced in clinical cases of bacterial infection.

Med Microbiol. 1995 Jan;42(1):62-6

Killing of methicillin-resistant Staphylococcus aureus by low-power laser light.

Wilson M, Yianni C.

Department of Microbiology, Eastman Dental Institute for Oral Health Sciences, University of London.

The purpose of this study was to determine whether a methicillin-resistant strain of Staphylococcus aureus (MRSA) could be sensitised by toluidine blue O (TBO) to killing by light from a low-power helium/neon (HeNe) laser. Suspensions containing c. 10(10) cfu of MRSA were irradiated with light from a 35 mW HeNe laser (energy dose: 0.5-2.1 J) in the presence of TBO (1.6-12.5 micrograms/ml) and the survivors were enumerated. The kills attained depended on both the light energy dose and concentration of TBO employed. A 4.47 log10 reduction in the viable count was achieved with a TBO concentration of 12.5 micrograms/ml and a light dose of 2.1 J (energy density 43 J/cm2). MRSA were susceptible to killing by the laser light within 30 s of exposure to the TBO. The results of this study have demonstrated that MRSA can be rapidly sensitised by TBO to killing by HeNe laser light and that killing depends on the light energy dose and sensitiser concentration.