The effect of sublethal photodynamic therapy on the expression of Enterococcal surface protein (esp) encoding gene in...

During antimicrobial photodynamic therapy (aPDT) in the treatment of endodontic intracanal infection, it is extremely likely that microorganisms would be exposed to sub-lethal doses of PDT (sPDT). Although sPDT would not result in microorganism death, it can considerably influence microbial virulence. This study evaluated the effect of sPDT on gene expression of Enterococci surface protein (esp) as a major virulence factor for biofilm formation in Enterococcus faecalis.

The lethal and sub-lethal potential of aPDT using indocyanine green (ICG), toluidine blue O (TBO), and methylene blue (MB), as the photosensitizers (PSs) and 660, 635, and 810 nm diode laser against E. faecalis was analyzed using colony-forming unit assays. Considering sub-lethal doses of PSs and photo-irradiation time of the diode laser, the expression of esp was evaluated through quantitative Real-time PCR (qRT-PCR).

ICG at a concentration of 31.2-1000 μg/mL and both TBO and MB at 6.2-100 μg/mL significantly reducedE. faecalis growth. 660, 635, and 810 nm diode laser with energy density of 93.75-140.62, 137.5-206.25, and 31.25-62.5 J/cm², reduced the bacterial count. ICG with a concentration of 15.6 μg/mL and irradiation time of 0.5 min, TBO with a concentration of 3.1 μg/mL and irradiation time of 3 min, and MB with a concentration of 3.1 μg/mL and irradiation time of 3 min were found as a sPDT dose against E. faecalis. The esp expression was significantly reduced at sub-lethal doses of ICG compared to TBO (2 fold) and MB (2.4 fold).

Although all tested PSs showed bacterial reduction, ICG may be considered as the best PS in treating endodontic infection due to its higher efficacy in reduction of esp expression which has a main role in biofilm formation of E. faecalis.