Blue-light phototherapy kills antibiotic-resistant bacteria

Blue light has powerful bacteria-killing ability in the laboratory, and now its potent antibacterial effects have been demonstrated in human and animal tissues, according to a series of articles in Photomedicine and Laser Surgery.

“Bacterial resistance to drugs poses a major health care problem,” wrote Dr. Chukuka S. Enwemeka in the accompanying editorial, citing the growing number of deadly outbreaks worldwide of methicillin-resistant Staphylococcus aureus (MRSA). Enwemeka, dean of the College of Health Sciences at the University of Wisconsin-Milwaukee, is the journal’s co-editor-in-chief.

Blue light at 405 to 470 nm is bactericidal and could help stem the ongoing pandemic of MRSA and other bacterial infections, Enwemeka wrote.

Photomedicine and Laser Surgery is published online monthly. Courtesy of ©2013, Mary Ann Liebert Inc., publishers.

In the article “Effects of Photodynamic Therapy on Gram-Positive and Gram-Negative Bacterial Biofilms by Bioluminescence Imaging and Scanning Electron Microscopic Analysis” (doi: 10.1089/pho.2012.3341), Dr. Aguinaldo S. Garcez of São Leopoldo Mandic Dental Research Center in Brazil and co-authors show that photodynamic therapy and methylene blue delivered directly into the root canal of a human tooth infected with a bacterial biofilm destroyed both gram-positive and gram-negative bacteria, disrupted the biofilms and reduced the number of bacteria adhering to the tooth.

In another article, “Preliminary Assessment of Photoactivated Antimicrobial Collagen on Bioburden in a Murine Pressure Ulcer Model” (doi: 10.1089/pho.2012.3423), Dr. Raymond J. Lanza-fame of the Rochester (N.Y.) General Hospital Laser Center 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, the authors reported.

In a third article, “Wavelength and Bacterial Density Influence the Bactericidal Effect of Blue Light on Methicillin-Resistant Staphylococcus aureus (MRSA)” (doi: 10.1089/pho.2012.3461), Dr. Violet Bumah of the University of Wisconsin-Milwaukee and co-authors compared the bacteria-killing power of 405-nm versus 470-nm light on colonies of resistant Staphylococcus aureus, and how the density of the bacterial colonies could limit light penetration and the bactericidal effects of treatment.