Diversity of Endodontic Enterococcus faecalis from Brazil with a High Occurrence of the ST 397 Clone

Enterococcus faecalis is a common cause of nosocomial infections and is frequently associated with endodontic infections. However, there is a scarcity of studies addressing the genetic characterization of E. faecalis lineages most commonly associated with root canals. The aim of this study was to assess the genetic relatedness of E. faecalis strains from primary endodontic infections in Southeast Brazil, test the hypothesis of clones infecting unrelated individuals, and examine the antimicrobial resistance profile. The genetic relationship of 32 endodontic E. faecalis isolates was investigated using multilocus sequence typing (MLST). These isolates were collected from unrelated patients with primary endodontic infections treated in Brazil between 2010 and 2023. Antimicrobial susceptibility testing was performed using the disk diffusion method in accordance with the Clinical Laboratory Standards Institute guidelines. Twelve sequence types (STs) were detected, of which eight STs contained only a single strain. Clones of ST 30, ST 40, ST 97, and ST 397 were identified, with a notably high frequency of ST 397 (15/32). Susceptibility to the antimicrobial agents tested varied, with the highest resistance rates observed for clindamycin (100%), tetracycline (34.4%), azithromycin (31.2%), and ciprofloxacin (19.2%). One isolate was found to be multidrug-resistant. MLST analysis of endodontic E. faecalis revealed clones infecting different individuals in various cities over a span of up to 10 years, with a high occurrence of ST 397. Therefore, there appears to be a predominant E. faecalis lineage associated with endodontic infections in Southeast Brazil. These findings, together with existing literature, raise concerns that certain lineages may be specialized in causing endodontic infections.