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BMC Microbiology

, 13:201

First Online: 06 September 2013Received: 10 April 2013Accepted: 02 September 2013DOI: 10.1186-1471-2180-13-201

Cite this article as: Tubby, S., Wilson, M., Wright, J.A. et al. BMC Microbiol 2013 13: 201. doi:10.1186-1471-2180-13-201


BackgroundAntibiotic therapy can select for small colony variants of Staphylococcus aureus that are more resistant to antibiotics and can result in persistent infections, necessitating the development of more effective antimicrobial strategies to combat small colony variant infections. Photodynamic therapy is an alternative treatment approach which utilises light in combination with a light-activated antimicrobial agent to kill bacteria via a non-specific mechanism of action. In this study, we investigated whether the combination of 665 nm laser light and the light-activated antimicrobial agent methylene blue was able to successfully kill S. aureus small colony variants. S. aureus and isogenic stable small colony variant were exposed to varying doses 1.93 to 9.65 J-cm of 665 nm laser light in the presence of varying concentrations 1 to 20 μM of methylene blue.

ResultsThe combination of 665 nm laser light and methylene blue was found to be an effective strategy for the killing of small colony variants. At the highest light dose 9.65 J-cm and methylene blue concentration 20 μM tested, the number of viable bacteria decreased by approximately 6.9 log10 for the wild type and approximately 5 log10 for the small colony variant.

ConclusionsThese results suggest that photodynamic therapy has potential for use in the treatment of superficial infections caused by small colony variants of S. aureus and supports further research in this field.

KeywordsStaphylococcus aureus Lethal photosensitisation Photodynamic therapy Small colony variant Electronic supplementary materialThe online version of this article doi:10.1186-1471-2180-13-201 contains supplementary material, which is available to authorized users.

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Autor: Sarah Tubby - Michael Wilson - John A Wright - Ping Zhang - Sean P Nair


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