Effects of a Chimeric Lysin against Planktonic and Sessile Enterococcus faecalis Hint at Potential Application in Endodontic Therapy

Enterococcus faecalis is a commensal opportunistic pathogen found in the intestine, mouth, and vaginal tract of humans. As an invasive pathogen in the oral cavity, E. faecalis is one of the leading causes of periapical endodontic lesions. However, due to the strong biofilm-forming capacity and tolerance of E. faecalis to conventional antibiotics and treatments, limited therapeutic options are available. In the present study, we investigated the activity of ClyR, a chimeric lysin with extended streptococcal lytic spectrum, against planktonic and sessile E. faecalis cells in vitro and in an ex vivo dental model. Our results showed that ClyR has robust and rapid lytic activity against multiple E. faecalis strains, killing >90% planktonic cells within 1 min at a concentration of 50 μg/mL. The biochemical experiments combined with microscopy analysis revealed that ClyR degrades E. faecalis biofilm with high efficacy in a dose-dependent manner, reducing the survival rate to <40% within biofilms after treatment with 50 μg/mL ClyR for 1 h. In the ex vivo dental model, ClyR showed a significant biofilm removal efficacy, killing >90% viable bacteria within biofilms at a low dose of 50 μg/mL, which is much better than ampicillin and similar to calcium hydroxide, the extensively used routine intracanal medicament in the treatment of endodontics and dental traumatology. The robust activity of ClyR against both planktonic and sessile E. faecalis suggests the potential of ClyR in treating endodontic infections caused by E. faecalis.