Study of Genetic Determinants of Antibiotic Resistance in Endodontic Pathogen; Enterococcus faecalis

Abstract

Enterococcus faecalis is a resilient Gram-positive bacterium commonly associated with persistent infections in endodontics, including root canal treatment failures. This dissertation explores the genetic determinants of antibiotic resistance and persister formation in E. faecalis, as well as its survival strategies under antibiotic stress. Understanding these mechanisms is essential for developing more effective therapeutic approaches in endodontic and clinical settings. Chapter 1 provides an overview of E. faecalis as a significant pathogen in endodontics, detailing its ability to survive harsh environments and form biofilms, which contribute to its persistence in root canals. The chapter further discusses the bacterium’s intrinsic resistance to common antibiotics and its ability to acquire resistance genes through horizontal gene transfer, with a focus on vancomycin-resistant strains. Additionally, the phenomenon of persister cell formation, which allows E. faecalis to survive in a dormant state under antibiotic pressure, is introduced as a key factor in treatment failure. Chapter 2 investigates the genetic basis of persister formation in E. faecalis using the Dunny transposon mutant library. The library, containing mutants covering approximately 70% of the E. faecalis genome, was screened for genes associated with persister formation under antibiotic stress. Genes such as PhoU, uvrD/REP, and Fis were identified as potential candidates for regulating persister formation. However, experimental results showed no significant difference in persister formation between knockout mutants and the wild-type strain, suggesting that other genetic factors may play a critical role in this process. Chapter 3 focuses on the identification of antibiotic resistance genes in E. faecalis using the same transposon mutant library. A screening for resistance to ampicillin led to the identification of several mutants with resistance-associated genes, including sensor histidine kinases and phosphate-binding proteins. These findings highlight the complexity of resistance mechanisms in E. faecalis, with metabolic regulation, stress responses, and biofilm formation playing integral roles in survival under antibiotic pressure. Chapter 4 presents experiments assessing the microbial contamination and disinfection efficacy of gutta-percha (GP) cones in endodontics. While GP cones are generally clean, they can harbor bacteria, which may lead to infections if not properly disinfected. The effectiveness of sodium hypochlorite (NaOCl) as a disinfecting agent was evaluated in clinical settings. 16S rRNA sequencing revealed that NaOCl treatment significantly reduced bacterial contamination on GP cones, underscoring the importance of disinfection protocols in preventing infection during root canal therapy. This dissertation provides insights into the genetic determinants of antibiotic resistance and persister formation in E. faecalis, contributing to the understanding of its role in endodontic infections. It also emphasizes the need for improved disinfection strategies to ensure the safety and success of root canal treatments. Further exploration of the genetic factors involved in E. faecalis persistence and resistance is necessary to develop novel therapeutic strategies to combat this challenging pathogen.