Immunogenic Potential of Enterococcus faecalis Biofilm under Simulated Growth Conditions

Abstract

Introduction: The aim of this study was to evaluate the effect of growth modes (planktonic and biofilms) of Enterococcus faecalis on the intracellular survival and ability to produce tumor necrosis factor α (TNF-α) and interleukin (IL)-6 after interacting with monocytes/in vitro-differentiated macrophages. Methods: In vitro biofilms of three E. faecalis strains (ATCC-29212, OG1RF, and FA2-2) were grown on dentin under simulated nutrient-rich and nutrient-deprived conditions. Biofilm-derived E. faecalis cells were incubated with monocytes/in vitro-differentiated human macrophages. A fluorometric assay was used to quantify the surface adherent bacteria, whereas an antibiotic protection assay was used to quantify the internalized E. faecalis cells 6 to 48 hours after interaction with macrophages. TNF-α and IL-6 produced during this interaction were quantified by an enzyme-linked immunosorbent assay. Results: The surface adherence and intracellular survival of E. faecalis within macrophages was significantly higher in biofilm bacteria when compared with planktonic cells (p ≤ 0.05). E. faecalis strains survived within the macrophages for up to 48 hours and produced higher levels of IL-6 with planktonic cells when compared with biofilm cells. Except in FA2-2, the planktonic cells of other strains did not show a significant increase in TNF-α compared with the biofilm cells (p > 0.05). Conclusion: Biofilm cells of E. faecalis interacting with macrophages showed higher potential for surface adherence, intracellular survival and produced lesser amounts of IL-6 and TNF-α when compared to planktonic cells. Further experiments are required to understand the clinical implication of the intracellular survival of E. faecalis biofilm. © 2010 American Association of Endodontists.