Enterococcus faecalis

Enterococcus faecalis – formerly classified as part of the group D Streptococcus, is a Gram-positive, commensal bacterium naturally inhabiting the gastrointestinal tracts of humans. Like other species in the genus Enterococcus, E. faecalis is found in healthy humans and can be used as a probiotic. The probiotic strains such as Symbioflor1 and EF-2001 are characterized by the lack of specific genes related to drug resistance and pathogenesis. Despite its commensal role, E. faecalis is an opportunistic pathogen that can cause severe infections, especially in nosocomial (hospital) settings. Enterococcus spp. is among the leading causes of healthcare-associated infections ranging from endocarditis to urinary tract infections (UTIs). Hospital-acquired UTIs are associated with catheterization because catheters provide an ideal surface for biofilm formation, allowing E. faecalis to adhere, persist, and evade both the immune response and antibiotic treatment. E. faecalis can grow in extreme environments due to its highly adaptive genome and lack of strong defense mechanisms. Its ability to easily acquire and transfer genes across species contributes to rising antibiotic resistance. E. faecalis exhibits intrinsic resistance to multiple antibiotics, including oxazolidinones, quinolones, and most β-lactams, such as cephalosporins. E. faecalis has been frequently found in reinfected root canal-treated teeth, with a prevalence ranging from 30% to 90%. Re-infected root canal-treated teeth are about nine times more likely to harbor E. faecalis than cases of primary infections.