Activated Oxygen may kill antibiotic-resistant bacteria

Oxygen-activated by specially formulated photosensitizing light can kill antibiotic-resistant bacteria such as methicillin-resistant Staphylococcus aureus (MRSA), according to the findings of the research presented at the 256th National Meeting & Exposition of the American Chemical Society (ACS). The method can be used as an alternative to antibiotics to treat other microbial infections, and possibly even cancer.

At present few alternatives are available for patients to get rid of MRSA such as hiring infection prevention staff to track hand hygiene and disinfecting every patient admitted to an acute-care setting which cut the rate of bloodstream infections in half. However, this procedure isn't feasible in most hospitals.

"Instead of resorting to antibiotics, which no longer work against some bacteria like MRSA, we use photosensitizers, mostly dye molecules, that become excited when illuminated with light," Peng Zhang, Ph.D., says. "Then, the photosensitizers convert oxygen into reactive oxygen species that attack the bacteria."

Photosensitizers in a molecular form tend to not be corralled enough to do significant damage. In addition, many of them are hydrophobic. This makes it difficult to disperse them in aqueous media where microorganisms typically exist. The researchers set out to design a new, water-dispersible, hybrid photosensitizer -- one that includes noble metal nanoparticles decorated with amphiphilic polymers to entrap the molecular photosensitizers. To activate and use it, medical professionals would illuminate the product with blue or red light.

The team showed that the new nanoparticle photosensitizer was much more effective at killing a variety of bacteria than corresponding formulations that did not contain the metal particles. According to Zhang, these nanoparticles provide two benefits. The metal has a plasmonic enhancement effect that promotes the generation of more reactive oxygen species, while also concentrating the photosensitizers in one place for a more localized hit to the bacterial cells.

Zhang explains it this way: "If you want to attack a castle, and you just let all these people attack individually, it is not very effective. Instead, if you have the same number of people grouped together attacking the castle at one point, it is possible to cause more damage."

Zhang has a patent related to the design of hybrid photosensitizers, which can be formulated into a spray or gel. Zhang said that apart from eradicating MRSA, the nanoparticles are ideal for destroying skin cancer cells. The nanoparticles perform effectively with the illumination of red light, which has a long wavelength that penetrates deep below the skin and may be effective in skin cancer treatment. The nanoparticles have also been shown to eliminate nail bed fungus.