A growing problem is that bacteria, like most organisms,
evolve to combat things that are dangerous to them. This has produced strains
of bacteria that no longer respond to treatments that once hindered their
growth. While advances such as MIT's bacteria
resistant polymer will surely help prevent hospital-caused infection, it
does not help treat them once they've taken root, nor can it do much against
infections caused from accidents in less clean environments.
That's where lasers come in to diffuse the situation. While the statement
conjures up visions similar to Johns Hopkins's virus
busting laser, raining beams of bacterial genocide down upon an infection,
it's a lot less difficult than that. In fact, the laser in this case doesn't
even need to make contact with the bacteria to do the job. Instead, a harmless
dye known as indocyanine green is what brings a quick end to the harmful
invaders. Or more specifically, what happens to the dye when it's activated by a
The effect is similar to Rensselaer Polytechnic Institute's cancer
killing nanoparticle treatment. When a laser, in this case a 500mW
gallium-aluminum-arsenide near-infrared laser projecting at 808nm wavelength,
is shined at a photosensitizer, the indocyanine green, it creates free radicals
known as reactive oxygen species. These free radicals destroy bacteria by
disrupting numerous parts of their physiology.
One benefit to this method is that it is very unlikely a strain of bacteria
could develop a resistance to this type of treatment. Too many parts of the
bacteria are affected simultaneously. Bacteria develop resistance to antibiotics
by changing whatever part of their anatomy that the antibiotic affects,
evolving to counteract it much the same way insects evolve to live undaunted by
pesticides used to treat farm crops.
Another positive quality of this treatment involves the penetration properties
of the near-infrared laser. While the duration and power do not cause
temperature fluctuations like more powerful infrared lasers, the wavelength
allows the wave to pass through a limited amount of flesh, reaching subcutaneous
areas, allowing non surface bacteria to be destroyed as well, provided the dye
can be absorbed into the area.
The University College of London team that developed the technology has used
the technique to successfully destroy at least three different strains of
bacteria: Gram-negative Pseudomonas aeruginosa, the most common type of
burn infection; Gram-positive Staphylococcus aureus; and Streptococcus
An abstract of
their findings can be found at Biomed Central, along with an unformatted
PDF titled “Lethal photosensitization of wound-associated microbes using
indocyanine green and near-infrared light” which explains the process and
results in depth.