29th Annual Meeting of the American Society of Photobiology

Downtown Marriot

Chicago, Il.

The Interaction between the Phenothiazine Dyes as Photosensitizers and Gram Negative Bacteria and their Lipopolysaccharides

Abstract-
We have previously shown that the dimers of the phenothiazine dyes, Methylene Blue (MB) and Toluidine Blue (TB), participate in the photokilling of bacteria along with the dye monomers. Dye dimers appear to have a greater involvement in photokilling of gram-negative bacteria. As soon as dye was added to a bacterial suspension, dye dimerization was induced by the chromotropes of the bacterial cell. This resulted in a metachromatic effect of the dye absorption spectra. In order to elucidate what kind of bacterial cell surface biopolymer might participate in the reaction with the dye, we investigated the behavior of the MB and TB absorption spectra in the presence of both the gram negative bacteria and the lipopolysaccharides (LPS) extracted from the following bacteria: Pseudomonas aeruginosa, Escherchia coli, Klebsiella pneumoniae, and Serratia marcescens. It was shown that the dye absorbance of the monomer band maximum depended on the bacterial or LPS concentration. Information about the positions of the minimum and the depth of the spectral curves in the presence of both gram negatives and LPS was obtained. In addition, the relative dimerization constants of MB and TB in the presence of bacteria or LPS were calculated. The comparative analysis of the spectral characteristics of each dye in the presence of both bacteria and LPS indicates the similarity in the behavior of each dye induced by both the bacteria and LPS. The relationship between the intensity of the metachromatic reaction between the dye and the bacteria, the dye and appropriate LPS and the dye photobactericidal efficacy is discussed.

Keywords: Methylene Blue, Toluidine Blue, photosensitizer, gram negative bacteria, lipopolysaccharide