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Proceedings Paper

Anthrax surrogate spores are destroyed by PDT mediated by phenothiazinium dyes
Author(s): Tatiana N. Demidova; Michael R. Hamblin
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Paper Abstract

Some Gram-positive bacteria (including the causative agent of anthrax - Bacillus anthracis) survive conditions of stress and starvation by producing dormant stage spores. The spore’s multilayered capsule consists of inner and outer membranes, cortex, proteinaceous spore coat, and in some species an exosporium. These outer layers enclose dehydrated and condensed DNA, saturated with small, acid-soluble proteins. These protective structures make spores highly resistant to damage by heat, radiation, and commonly employed anti-bacterial agents. Previously Bacillus spores have been shown to be resistant to photodynamic inactivation (PDI) using dyes and light that easily destroy the corresponding vegetative bacteria, but recently we have discovered that they are susceptible to PDI. Photoinactivation, however, is only possible if phenothiazinium dyes are used. Dimethylmethylene blue, methylene blue, new methylene blue and toluidine blue O are all effective photosensitizers. Alternative photosensitizers such as Rose Bengal, polylysine chlorin(e6) conjugate, a tricationic porphyrin and benzoporphyrin derivative are ineffective against spores even though they can easily kill vegetative cells. Spores of B. cereus and B. thuringiensis are most susceptible, B. subtilis and B. atrophaeus are also killed, while B. megaterium is resistant. Photoinactivation is most effective when excess dye is washed from the spores showing that the dye binds to the spores and that excess dye in solution can quench light delivery. The relatively mild conditions needed for spore killing could have applications for treating wounds contaminated by anthrax spores and for which conventional sporicides would have unacceptable tissue toxicity.

Paper Details

Date Published: 8 April 2005
PDF: 12 pages
Proc. SPIE 5689, Optical Methods for Tumor Treatment and Detection: Mechanisms and Techniques in Photodynamic Therapy XIV, (8 April 2005); doi: 10.1117/12.589324
Show Author Affiliations
Tatiana N. Demidova, Wellman Ctr. for Photomedicine, Massachusetts General Hospital (United States)
Tufts Univ. (United States)
Michael R. Hamblin, Wellman Ctr. for Photomedicine, Massachusetts General Hospital (United States)
Harvard Medical School (United States)


Published in SPIE Proceedings Vol. 5689:
Optical Methods for Tumor Treatment and Detection: Mechanisms and Techniques in Photodynamic Therapy XIV
David Kessel, Editor(s)

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