21 February 2008 Photosensitization of Aggregatibacter actinomycetemcomitans with methylene blue: a microbiological and spectroscopic study
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Abstract
The aim of this study was to determinate the efficiency of methylene blue (MB) to kill cultures of Aggregatibacter actinomycetemcomitans under red light and to investigate MB photobleaching by optical absorption spectroscopy. Bacteria were diluted in aqueous solution, putted in glass tubes and distributed in 5 groups: (L-MB-) control group; (L+MB-) laser alone by 5min; (L-MB+) MB alone through 5min; (3L+MB+) MB+laser 3min; (5L+MB+) MB+laser 5min. Laser parameters were P=30mW, λ=660nm, E=9J in 5min and E=5.4J in 3min. The samples were diluted and bacterial colonies were counted and converted into colony forming units (CFU). Absorption spectra of the MB-stained bacterial suspension and photosensitized bacterial suspension were obtained. Groups L-MB-, L+MB-, and L-MB+ did not show a decrease in CFU/mL. L+MB+ groups showed a significant decrease in CFU/mL but no statistically significant differences were observed between 3min and 5min. Spectroscopy showed that MB is photodegraded after irradiation and that dimer species are more notably consumed than monomeric species. These results suggest that MB is a suitable photosensitizer to reduce A. actinomycetemcomitans, and that 3min of irradiation are enough to produce a significant effect. Due to the spectral changes observed on MB solution after irradiation a type I mechanism may be involved.
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Aécio M. Yamada Júnior, Renato A. Prates, Silvana Cai, Martha S. Ribeiro, "Photosensitization of Aggregatibacter actinomycetemcomitans with methylene blue: a microbiological and spectroscopic study", Proc. SPIE 6846, Mechanisms for Low-Light Therapy III, 68460F (21 February 2008); doi: 10.1117/12.763648; https://doi.org/10.1117/12.763648
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