Author: Roger Andersen, MD, MPH, RAC
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The science of photodisinfection has a fascinating history.
There is actually literature dating back to 1500 BC describing therapy involving the placement of certain kinds of seeds on the skin which were then exposed to sunlight. These seeds contained a psoralen compound, which has since been shown to be a photosensitizing compound. Since that time there are numerous conditions which have been shown to benefit from the therapeutic effects of light, such as cutaneous tuberculosis, psoriasis, cancerous tumors, vascular disease, newborn jaundice, and macular degeneration.
In the early 1990’s, it was found that photosensitizers could be used in combination with light to kill microorganisms, and indeed bacteria, yeasts, and viruses can be inactivated in this way. Cationic sensitizers have been proven to kill both Gram-positive and Gram-negative bacteria in the presence of light.
Following the application of certain bacteriological stains to infected areas it is possible to stain the bacteria and then apply a light source that is wavelength matched to the area. This causes a photochemical reaction that creates singlet oxygen free radicals from the surrounding tissue oxygen which in turn is lethally toxic to bacterial cells causing them to rupture their cell wall membrane.
A key potential benefit to this therapeutic approach is that it can be done in place of antibiotic therapy. Since there is no known mechanism for bacterial cells to become resistant to this therapy it has considerable benefit in cases of multidrug resistant (MDR) organisms such as methicillin-resistant Staphylococcus aureus(MRSA). Using non-antibiotic approaches to infections will allow antibiotics to be saved for those situations in which they are truly necessary.
The early work in this area was done by Dr. Michael Wilson at University College London in the mid-1990’s when he showed that oral pathogens could be killed using this approach. Recently the first commercial application of this technology has been introduced to Canada for the treatment of chronic periodontal disease and gingivitis by Ondine Biopharma of Vancouver, BC (www.ondinebiopharma.com).
In March of 2007, Health Canada also approved this therapy for the decolonization of MRSA from the nose. It has been shown that a large number of people unknowingly carry the MRSA organism in their nose. While this may not cause them any noticeable problems it may be accidently passed on to someone who may suffer an infection from it or if they were to go into the hospital for surgery they could possibly infect themselves. For instance, in a hospital situation, if health care workers are colonized with MRSA in their nose they may spread it around the hospital environment thus exposing patients to possible infection. With this new, quick, non-antibiotic approach it may be possible to easily disinfect both patients and staff and assist in bringing down the hospital acquired infection rate along with other hygienic measures such as frequent hand washing.
Future uses for photodynamic therapy in the treatment of infections could be for wounds, bedsores, ulcers, toenail fungus, oral malodor and possibly even for systemic bloodstream infections.
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