Electrical enhancement of chlorhexidine efficacy against the periodontal pathogen Porphyromonas gingivalis within a biofilm

Electric currents have been shown to promote the antimicrobial effectiveness of several biocides against microbial biofilms. Therefore, the objective of this work was to test the null hypothesis that low electric direct currents (DC) do not influence chlorhexidine (CHX) efficacy against the periodontal pathogen Porphyromonas gingivalis within a biofilm. A brain heart infusion medium inoculated with Streptococcus gordonii and P gingivalis was perfused for 7 days in anaerobiosis through two modified Robbins devices (MRD) assembled in parallel. Biofilms grew on hydroxyapatite discs placed at the bottom of the MRD plugs, and were then treated for 10 min with either CHX or CHX/DC (1.5 mA or 10 mA). The bactericidal effect against biofilms was then evaluated by comparing the mean proportions of P gingivalis killed. In the first series of experiments (CHX +/- 1.5mA), the proportions of P gingivalis killed were 81.1% for biofilms undergoing CHX and 79.1% when they were additionally treated with 1.5 mA (p>0.05). In the second series (CHX +/- 10mA), the viability of Pgingivalis was reduced by 87.3% with CHX and 98.9% when CHX was supplemented with 10mA (p<0.01). The null hypothesis was rejected, since a significant enhancement of the chlorhexidine 0.2% efficacy against P. gingivalis was observed when applying 10mA currents.