In vivo killing of Staphylococcus aureus using a light-activated antimicrobial agent.
BACKGROUND
The widespread problem of antibiotic resistance in pathogens such as Staphylococcus aureus has prompted the search for new antimicrobial approaches. In this study we report for the first time the use of a light-activated antimicrobial agent, methylene blue, to kill an epidemic methicillin-resistant Staphylococcus aureus (EMRSA-16) strain in two mouse wound models.


RESULTS
Following irradiation of wounds with 360 J/cm(2) of laser light (670 nm) in the presence of 100 microg/ml of methylene blue, a 25-fold reduction in the number of viable EMRSA was seen. This was independent of the increase in temperature of the wounds associated with the treatment. Histological examination of the wounds revealed no difference between the photodynamic therapy (PDT)-treated wounds and the untreated wounds, all of which showed the same degree of inflammatory infiltration at 24 hours.


CONCLUSIONS
The results of this study demonstrate that PDT is effective at reducing the total number of viable EMRSA in a wound. This approach has promise as a means of treating wound infections caused by antibiotic-resistant microbes as well as for the elimination of such organisms from carriage sites.
Zolfaghari
Parjam S
PS
Bloomsbury Institute of Intensive Care Medicine, Wolfson Institute for Biomedical Research, University College London, London, UK. p.zolfaghari@ucl.ac.uk
Packer
Samantha
S
Singer
Mervyn
M
Nair
Sean P
SP
Bennett
Jon
J
Street
Cale
C
Wilson
Michael
M
D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D005260:Female; D006358:Hot Temperature; D008027:Light; D055624:Methicillin-Resistant Staphylococcus aureus / Q000528:radiation effects*; D008751:Methylene Blue / Q000494:pharmacology*; D051379:Mice; D010778:Photochemotherapy; D017319:Photosensitizing Agents / Q000494:pharmacology; D014946:Wound Infection / Q000382:microbiology*
D000900:Anti-Bacterial Agents; D017319:Photosensitizing Agents; D008751:Methylene Blue