Rose bengal-mediated photodynamic inactivation against periodontopathogens in vitro

The main goal of periodontal therapy is to eliminate the spread of infection in the periodontium. Antimicrobial photodynamic therapy (aPDT) is a bactericidal method that has been recently introduced for controlling periodontal infection. The aim of this in vitro study was to evaluate the effect of aPDT using a combination of medium-power blue light-emitting diodes (LEDs) and rose bengal (RB) on selected key periodontopathogens.

Porphyromonas gingivalis ATCC33277, Aggregatibacter actinomycetemcomitans ATCC29523 and Fusobacterium nucleatum ATCC10953 were used in the experiments. Each bacterial suspension was irradiated with a blue LED (BL) (450-470 nm, output power density of 1.2 W/cm²) for 20-60 s (6-18 J/cm²), treated with RB (1 min), or subjected to a combination of RB treatment and BL irradiation (40 s, 12 J/cm²). All bacterial suspensions were serially diluted, plated and incubated anaerobically or microaerobically, and the numbers of colony-forming units (CFUs) were counted on day 7. One-way analysis of variance (ANOVA) and Tukey's HSD tests were used for statistical analysis.

Treatment with BL irradiation from 6 to 18 J/cm² did not significantly reduce the number of CFUs, whereas treatment with RB alone induced a low-to-high reduction in the bacterial CFUs in a dye concentration-dependent manner. Furthermore, the difference in the effects obtained with 16 μg/mL and 160 μg/mL RB was not statistically significant. Treatment with the BL at 12 J/cm² combined with 160 μg/mL RB yielded maximal log reductions of 3.03, 4.2 and 2.23 in P. gingivalis, A. actinomycetemcomitans and F. nucleatum CFUs, respectively.

Within the limits of this study, the three periodontal pathogens, especially A. actinomycetemcomitans, were susceptible to photodynamic inactivation by the combination of the BL and RB. RB-mediated aPDT may offer a viable alternative tool for periodontal pathogen treatment, especially for A. actinomycetemcomitans eradication. aPDT may be a valuable tool for the treatment of periodontal diseases, particularly those in which A. actinomycetemcomitans is a dominating pathogen.