Method: E. faecalis, a persistent endodontic pathogen, in different modes of growth - planktonic suspension, co-aggregated with Actinomyces israelii and in 4-day old biofilms was tested in the study. Aqueous Ca(OH)2 in concentrations of 25%, 50% and 100% for 3, 12 and 24 hours of exposure and Methylene Blue (MB) mediated LAD at a fluence range of 2 – 40 J/cm2 were conducted. To evaluate the role of efflux pumps, an Efflux Pump Inhibitor (EPI) was incorporated into both modalities of treatment. The antimicrobial activity was assessed by determining the colony-forming units remaining after treatment. Statistical analysis was conducted by Kruskal–Wallis one-way analysis of variance and Mann–Whitney U-tests along with Student's t-test.
Results: The order of susceptibility to Ca(OH)2 and LAD was: planktonic > co-aggregated suspension > biofilm. E. faecalis in a planktonic and co-aggregated suspension was susceptible to killing by Ca(OH)2 with a 100% solution showing complete killing by 3 hours (p<0.001). E. faecalis in biofilms persisted in high numbers even after a 24 hour exposure to all the concentrations tested. The antibacterial effect on E. faecalis biofilms was enhanced with the use of an EPI along with lower concentrations of Ca(OH)2 (p<0.05) and with a phenothiazinium photosensitizer (MB) for LAD (p<0.001) Conclusion: E. faecalis in a planktonic and co-aggregated suspension was more susceptible to killing by Ca(OH)2 and LAD than in a biofilm. The use of an EPI with lower concentrations of Ca(OH)2 and with a phenothiazinium photosensitizer (MB) for LAD resulted in a significant increase in the antibacterial effect.
(Supported by the NUS-ARF 224 000 024 112 and Research initiative: Dental Biophotonics and Biomaterials Programme (DBBP): C-221-000-304-001)