Immunogenic Potential of Enterococcus faecalis Biofilm under Simulated Growth Conditions

IntroductionThe 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.MethodsIn 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.ResultsThe 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).ConclusionBiofilm 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.