Antibody-targeted lethal photosensitization of Porphyromonas gingivalis

We have previously demonstrated that Porphyromonas gingivalis is susceptibl e to killing by toluidine blue O (TBO) when irradiated with light from a he lium-neon (HeNe) laser. The aim of this study was to determine whether a TB O-antibody conjugate (Ab-TBO) could be used to specifically target P. gingi valis to lethal photosensitization in the presence of Streptococcus sanguis or human gingival fibroblasts (HGFs). When a mixture of P. gingivalis and S. sanguis was exposed to 4 mu g of TBO/ml and irradiated with HeNe laser l ight, there were 1.5- and 4.0-log(10)-unit reductions in the viable counts, respectively. In contrast, when TBO was conjugated with a murine monoclona l antibody against P. gingivalis lipopolysaccharide, the reductions in viab le counts of P. gingivalis and S. sanguis amounted to 5.0 and 0.1 log(10) u nits, respectively. Lethal photosensitization of P. gingivalis in the prese nce of HGFs using unconjugated TBO resulted in a 0.7-log(10)-unit reduction in P. gingivalis viable counts and a 99% reduction in the incorporation of tritiated thymidine ([H-3]Tdr) by the HGFs, In contrast, when the Ab TBO c onjugate was used, there was a 100% reduction in P. gingivalis viable count s but no significant reduction in the incorporation of [H-3]Tdr by HGFs, Th ese results demonstrate that specific targeting of P. gingivalis can be ach ieved using TBO conjugated to a monoclonal antibody raised against a cell s urface component of this organism.