Therapeutic Potential of Gramicidin S in the Treatment of Root Canal Infections

An intrinsic clindamycin-resistant Enterococcus faecalis, the most common single species present in teeth after failed root canal therapy, often possesses acquired tetracycline resistance. In these cases, root canal infections are commonly treated with Ledermix(®) paste, which contains demeclocycline, or the new alternative endodontic paste Odontopaste, which contains clindamycin; however, these treatments are often ineffective. We studied the killing activity of the cyclic antimicrobial peptide gramicidin S (GS) against planktonic and biofilm cells of tetracycline-resistant clinical isolates of E. faecalis. The high therapeutic potential of GS for the topical treatment of problematic teeth is based on the rapid bactericidal effect toward the biofilm-forming, tetracycline-resistant E. faecalis. GS reduces the cell number of planktonic cells within 20–40 min at a concentration of 40–80 μg/mL. It kills the cells of pre-grown biofilms at concentrations of 100–200 μg/mL, such that no re-growth is possible. The translocation of the peptide into the cell interior and its complexation with intracellular nucleotides, including the alarmon ppGpp, can explain its anti-biofilm effect. The successful treatment of persistently infected root canals of two volunteers confirms the high effectiveness of GS. The broad GS activity towards resistant, biofilm-forming E. faecalis suggests its applications for approval in root canal medication.