Antimicrobial Efficacy of Photodynamic Therapy and Sodium Hypochlorite on Monoculture Biofilms of Enterococcus faecalis at Different Stages of Development

Abstract

As the Enterococcus faecalis biofilm ages, it is likely that bacteria in mature and old biofilms will become more resistant to commonly used antibacterial irrigants. Photodynamic therapy (PDT) has been used to kill resistant bacteria organized in a biofilm. This study aimed to investigate the antimicrobial effectiveness of 1% sodium hypochlorite (NaOCl), 2.5% NaOCl, and PDT on E. faecalis biofilm at different stages of development. In this study 4-, 6-, and 8-week-old E. faecalis biofilms were subjected to one of the following approaches: phosphate-buffered saline solution (PBS), PDT, or 1% and 2.5% NaOCl. Dentin chip suspensions were used for colony forming units (CFU) counting to estimate remaining E. faecalis counts. PDT and 2.5% NaOCl completely eliminated E. faecalis biofilms in three stages of biofilm development, whereas 1% NaOCl resulted in 81.88%, 85.73%, and 78.62% reductions of bacterial counts in 4-, 6-, and 8-week-old biofilms, respectively, which was significantly more than PBS. The bacteria in mature and old biofilms were more resistant to 1% NaOCl than were the bacteria in young biofilms. Overall survival and residual bacteria increase with biofilm aging. PDT and the 2.5% NaOCl solution were equally efficient in completely eliminating E. faecalis biofilms at all three stages.