Ex vivo assessment of synergic effect of chlorhexidine for enhancing antimicrobial photodynamic therapy efficiency on expression patterns of biofilm-associated genes of Enterococcus faecalis

Background: It has clearly been demonstrated that Enterococcus faecalis, as a persistent microorganism, is the major agent in the etiopatogeny of endodontic infections. Recently, the limitations of conventional endodontic therapy have given rise to many attempts to introduce antimicrobial photodynamic therapy (aPDT) as an alternative treatment. The aim of this study was to analyze the ex vivo effect of aPDT in combination with 2.0% chlorhexidine (CHX) as a conventional therapy on colony count and expression patterns of genes associated with biofilm formation of E. faecalis. Materials and methods: A total of 125 extracted human single-rooted teeth were divide into six groups (A-F; n = 20) and were incubated with E. faecalis. Group A-photosensitizer (indocyanine green [ICG]); B-diode laser; C- aPDT; D- 2.0% CHX; E- aPDT with photosensitizer modified by 2.0% CHX; and F- control group (no procedure was performed). Five remaining teeth were used to confirm the presence of E. faecalis biofilm via scanning electron microscope. Counts of colony forming units (CFUs) in each group were evaluated separately and quantitative real-time PCR (qRT-PCR) was then applied to monitor genes expression of fsrC, efa, and gelE involved in E. faecalis biofilm. Results: The results showed that none of the tested groups achieved eradication or inhibition of biofilm. On the other hand, aPDT + 2.0% CHX, 2.0% CHX, and ICG-mediated aPDT groups showed significantly less CFU/mL than ICG and diode laser groups. The group with the lowest CFU/mL count was the aPDT + 2.0% CHX, being statistically different from all other groups that could decrease the expression levels of efa, gelE, and fsrC genes 6.8-, 8.3-, and 12.1-fold, respectively. Conclusion: Based on the results, the synergism effect of ICG-aPDT with 2.0% CHX leads to modulation of the virulence of E. faecalis strains biofilm model by suppressing the expression of the genes associated with biofilm formation.