Antibacterial effects of two synthetic peptides against Enterococcus faecalis biofilms: a preliminary in vitro study

Aim: Current endodontic techniques are unable to fully eradicate intracanal bacteria. Thus, new agents that effectively eliminate endodontic pathogens are needed. The aim of this study was to assess the antibacterial properties of two synthetic peptides, namely KP and L18R, against planktonic cells and biofilms of the endodontic pathogen Enterococcus faecalis. Methodology:KP and L18R bactericidal activity against E. faecalisATCC 29212 was evaluated by colony forming unit assays and the half maximal effective concentration (EC50) was calculated. The effect of peptides on E. faecalis biofilm formation onto polystyrene plates was also assessed by the crystal violet assay. Confocal laser scanning microscopy (CLSM) analysis was carried out to compare the effects of KP, L18R, and a Ca(OH)2saturated solution in an in vitro model of dental infection consisting in 2-day-old E. faecalisbiofilms grown on hydroxyapatite disks. Results: Both KP and L18R showed strong bactericidal activity against planktonic E. faecalis. L18R proved to be 10-folds more effective than KP (KP and L18R EC50values = 4.520 × 10‑6 Mand 3.624 × 10-7 M, respectively). Peptides inhibited E. faecalis biofilm formation in a dose-dependent manner and L18R resulted more effective than KP.CLSM images showed that Ca(OH)2, KP and L18R remarkably impaired E. faecalis biofilms pre-grown on hydroxyapatite. Conclusions: KP and L18R effectively inhibited E. faecalis, both in planktonic and biofilm form. L18R demonstrated a more potent antibacterial activity than KP. These preliminary results suggest that antimicrobial peptides may represent a promising new strategy for endodontic infection control.