# Therapeutic Potential of Gramicidin S in the Treatment of Root Canal Infections
## 3 Discussion
This was demonstrated in our killing assays of stationary cells (Figure 2), and in the biofilm re-growth experiments with each of the selected three strongest biofilm forming strains of _E. faecalis_ (Table 1 and Figure 1). The origin of _E. faecalis_ in the root canal is unclear, as enterococci do not belong to the normal oral microbial flora [7]. However, 77% of British-produced cheeses [37], 60% of French soft cheeses, and 20% of mozzarella, feta and Swiss Tlisiter cheese [38], contain enterococci. A genetic analysis of saliva, previously treated root canal samples, and of cheeses, using repetitive extragenic palindromic (REP)-PCR, revealed nine _E. faecalis_ genotypes in all specimens studied. The transitional colonization of the oral cavity after the consumption of cheese may thus be a possible reason for the prevalence of _E. faecalis_ in root canal infections [37; 38]. Tetracycline-resistant enterococcal or multispecies infections may provoke treatment failure, requiring tooth extraction, if the therapy using an intracanal Ledermix(r) paste dressing is applied [16]. Even if several bacteria cause the infection, a GS-containing dressing would be an unsurpassable choice for successful treatment due to the broad-spectrum activity of GS [30]. Although microbiological analysis was not performed in two above described medication cases, a cure using GS alone and in combination with PMB has been successfully achieved. Recently, we also reported that these two peptides exert a synergistic effect against multidrug-resistant strains and against biofilms of _P. aeruginosa_[39]. In the treatment of root canal infections caused by this pathogen, which is frequently isolated from treatment-resistant cases, we expect that the combination of GS/PMB could play a very promising role. Remarkably, the pain-alleviating effect, which we describe here for both medication cases, had been previously observed in Russian clinical trials as a characteristic property only of GS but not of the related tyrothricin complex [40]--a peptide mixture of the lineal gramicidin A and cyclic tyroclines [41]. This unique property of GS should thus be highly advantageous in the treatment of painful root canal infections. Biofilm formation is a key virulence factor in the pathogenicity of persistent _E. faecalis_ infections [42]. Nutrients such as hemin, vitamin K and glucose enhance biofilm formation. The tetracycline-resistant _E. faecalis_ strain TRE2 was the best biofilm former amongst all clinical isolates. The exposure of its pre-grown biofilm to an aqueous solution of GS showed a bactericidal effect (no re-growth of biofilms was observed, and no viable cells were found in this culture upon plating), and some drastic morphological alterations of the biofilm remnants were observed (Figure 3). Our results thus highlight the promising potential of GS in the successful treatment of root canal infections caused by tetracycline-resistant biofilms of _E. faecalis_. In persistent infections, these bacteria can penetrate the cellular and tissue barrier and thereby present an imminent risk to human health, causing further non-oral, life-threatening infections, such as bacteremia or endocarditis [6; 43]. Therefore, the successful treatment of root canal infections and their prevention are vital tasks. GS alone or in combination with PMB offers an opportunity to help patients with untreatable root canal infections, to save their natural teeth and to avoid high prosthetic costs.