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JAC Advance Access originally published online on May 30, 2006
Journal of Antimicrobial Chemotherapy 2006 58(1):190-192; doi:10.1093/jac/dkl205
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© The Author 2006. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

Enhancement of erythrosine-mediated photodynamic therapy of Streptococcus mutans biofilms by light fractionation

Daniel Metcalf{dagger}, Colin Robinson, Deirdre Devine and Simon Wood*

Division of Oral Biology, Leeds Dental Institute, University of Leeds, Clarendon Way Leeds LS2 9LU, UK

Received 14 February 2006; returned 15 April 2006; revised 24 April 2006; accepted 27 April 2006

*Corresponding author. Tel: +44-113-233-6159; Fax: +44-113-233-6548; E-mail: s.r.wood{at}leeds.ac.uk

Objectives: We aimed to increase the bacterial cell killing efficacy of erythrosine-mediated photodynamic therapy (PDT) of Streptococcus mutans biofilms by fractionating the delivered light dose into a series of shorter pulses.

Methods: S. mutans biofilms of 200 µm thickness were grown in a constant-depth film fermenter (CDFF). Biofilms were incubated with 22 µM erythrosine before being irradiated with white light for increasing periods of time. We also used light dose fractionation to deliver the same overall dose of light in a series of shorter pulses separated by dark periods. Bacterial cell killing as a result of each killing protocol was quantified by colony counting.

Results: A 2 log10 of bacterial cell killing was achieved with 5 min of continuous white light irradiation. For time periods longer than 5 min the amount of killing increased more slowly, which was probably due to photobleaching of the erythrosine. Fractionation of the light dose into 5x 1 min doses separated by dark recovery periods of 5 min increased the amount of bacterial killing by 1 log10 compared with 5 min continuous irradiation. Further fractionation of the light dose into 10x 30 s doses separated by 2 min recovery periods resulted in 3.7 log10 of cell kill, an improvement of 1.7 log10 compared with the continuous irradiation protocol.

Conclusions: Erythrosine-mediated PDT of S. mutans biofilms can be further enhanced by fractionation of the applied light dose.

Keywords: plaque , photosensitizers , PDT


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