Antimicrobial photodynamic therapy effectively reduces Porphyromonas gingivalis infection in gingival fibroblasts and keratinocytes: An in vitro study.

BACKGROUND

Porphyromonas gingivalis possess the ability to invade host cells which prevents this pathogen from eradication by conventional periodontal therapy. Recently, antimicrobial photodynamic therapy (aPDT) was introduced to periodontal treatment as a complementary antibacterial method. The aim of this study was to evaluate the effect of toluidine blue-O (TBO) mediated aPDT on the viability of P. gingivalis invading gingival fibroblasts and keratinocytes in an in vitro model of infection.

METHODS

Primary human gingival fibroblasts (PHGF) and telomerase immortalized gingival keratinocytes (TIGK) were infected with Pg ATCC 33277. Two concentrations of TBO (0.01 mg/mL, TBO-c1 and 0.001 mg/mL, TBO-c2) and a non-laser red light source (λ = 630 nm) were applied to treat both cell-adherent/intracellular Pg (the adhesion/invasion model) or exclusively the intracellular bacteria (the intracellular infection model).

RESULTS

The median viability of cell-adherent/intracellular Pg in infected keratinocytes declined from 1.88 × 10 cfu/mL in infected cells treated with TBO without irradiation to 40 cfu/mL upon irradiation for 10 s with TBO-c1. At higher light doses a complete photokilling of P. gingivalis was observed. Pg from exclusively intracellular infection model was also efficiently eradicated as the residual viability dropped from 1.44 × 10 cfu/mL in control samples to 160, 20 and 10 cfu/mL upon irradiation for 10, 20 and 30 s, respectively. In the infected fibroblasts irradiation significantly reduced bacterial viability but did not completely eradicate the intracellular pathogen.

CONCLUSIONS

Antimicrobial PDT is effective in reducing the viability of intracellular periopathogens, however those residing within gingival fibroblasts seems to attenuate the photokilling effectiveness of this method.