Treating MRSA, lightly

Rebecca C. Jernigan, rebecca.jernigan@laurin.com

Outbreaks of MRSA (methicillin-resistant Staphylococcus aureus) make the news on a regular basis. While staph infections are very common, the thought of facing an infection that is immune to the antibiotics most often used is frightening. It doesn’t help that the few antibiotics effective against the bacteria are extremely potent and could produce a range of negative side effects. Added to this is the fact that MRSA is no longer solely a “hospital bug” but can be transferred within the community. Recently, it was identified as having been transferred from human to elephant and back again, so it is understandable that people want faster, safer treatments.

Investigators at the New York Institute of Technology have demonstrated the use of 470-nm blue light as a possible treatment for MRSA, using the wavelength to destroy cultured colonies of the bacteria.

Photographs show colonies of hospital-acquired MRSA. The number on each plate represents the dose of 470-nm blue light in joules per centimeter squared. Image reprinted with permission from Photomedicine and Laser Surgery, 2009, published by Mary Ann Liebert Inc., New Rochelle, N.Y.

The group had previously demonstrated that 405-nm light could kill MRSA strains grown in culture, but 405-nm light contains a trace of ultraviolet, which can be damaging to human cells. By using 470-nm light, the scientists were able to achieve similar results without exposing their theoretical patients to ultraviolet light.

The researchers grew cultures of both a hospital-acquired strain (IS853) and a community-acquired strain (US300) of MRSA. Half the cultures were irradiated with blue light, while the other half served as controls. More than 90 percent of the bacteria were killed when exposed to a dose of 55 J/cm² – approximately 30 minutes of exposure to the light.

Chukuka Enwemeka, an investigator involved in the study, said that the finding that MRSA can be destroyed at low dosages of blue light could lead to a practical, inexpensive approach to bacteria treatment and eradication. Light could be used effectively against the common cutaneous or subcutaneous presentation of bacterial illness. The fact that both MRSA strains responded similarly to treatment indicates that the bacteria may not be able to develop a resistance to the approach.