Inactivation of Proteolytic Enzymes from Porphyromonas gingivalis Using Light-activated Agents

. Previous studies have shown one of the causative agents of periodontitis, Porphyromonas gingivalis, can be killed by red light in the presence of the light-activated antimicrobial agent toluidine blue O (TBO). The purpose of this study was to determine the effects of irradiating the organism with red light in the presence of TBO on its proteolytic enzyme activity. Suspensions of P. gingivalis were exposed to light with a wavelength of 633 nm in the presence of various concentrations of TBO. Samples were taken at various times and their proteolytic activity determined by assay of azocasein hydrolysis. On exposure to 126 J of red light in the presence of 12.5 μg/ml of TBO the proteolytic enzyme activity was reduced by 100%. The results of this study have shown that the main virulence factor of P. gingivalis, its proteolytic activity, can be inactivated by red light in the presence of TBO. This, together with the known bactericidal activity of the TBO/light combination, suggests that photodynamic therapy may prove important in reducing the effectiveness of P. gingivalis as a periodontopathogen in vivo. Paper received 24 June 1998; accepted after revision 20 June 1999.