Effect of trans-cinnamaldehyde on Enterococcus faecalis biofilms

Abstract

Objectives: Enterococcus faecalis forms strong biofilms that resist harsh environmental conditions, contributing to its survival and virulence in root canal infections. The objective of this study was to investigate the effect of a natural compound, trans-cinnamaldehyde (TC) on the metabolic activity of E. faecalis biofilms at different time points in the presence and absence of nutrients. The null hypothesis was that TC treatment does not significantly reduce the biofilm metabolic activity at any time point, compared to the control. Methods: Mature 3-day old E. faecalis ATCC 29212 biofilms were treated with TC (MBC, 2xMBC, 4xMBC) for 24 h. The biofilm metabolic activity was measured using XTT assay, immediately post-treatment (t0), and after incubating the biofilms for 48 (t1), 96 (t2) and 168 h (t3) in nutrient-rich [Brain Heat Infusion (BHI)] or nutrient-free [phosphate-buffered saline (PBS)] media. Dimethyl sulfoxide-treated biofilm served as the control. Statistical analysis was performed using Kruskal-Wallis and post-hoc Dunn tests (P=0.05). Architectural changes in the biofilm were studied using confocal laser scanning microscopy (CLSM). Results: The MBC of TC was 0.25% (w/v). TC at 0.5 and 1% significantly reduced the metabolic activity of biofilms compared to the control (P<0.001). No metabolic activity was detected in the presence of PBS, irrespective of the TC concentration and time (P>0.05). In the presence of BHI, 0.5 and 1% TC-treated biofilms showed a significant reduction in the metabolic activity at t1 and t2, compared to t0 (P<0.05). There was no significant difference between t0 and t3 (P>0.05). Treatment with 0.25% TC resulted in significantly higher metabolic activity at t1, t2 and t3 compared to t0 (P<0.05). CLSM revealed a concentration-dependent disruption of the biofilm architecture Conclusions: TC significantly decreased the metabolic activity of E. faecalis biofilms and sustained its effect up to 168 h. This effect was only observed under conditions supporting bacterial growth