Enterococcus faecalis – formerly classified as part of the group D Streptococcus system – is a Gram-positive, commensal bacterium inhabiting the gastrointestinal tracts of humans and other mammals. Like other species in the genusEnterococcus, E. faecalis is found in healthy humans, but can cause life-threatening infections, especially in the nosocomial environment, where the naturally high levels of antibiotic resistance found in E. faecalis contribute to its pathogenicity. E. faecalis has been frequently found in reinfected, root canal-treated teeth in prevalence values ranging from 30% to 90% of the cases. Re-infected root canal-treated teeth are about nine times more likely to harbor E. faecalis than cases of primary infections.
E. faecalis is found in most healthy individuals, but can cause endocarditis and sepsis, urinary tract infections, meningitis, and other infections in humans. Several virulence factors are thought to contribute to E. faecalis infections. A plasmid-encoded hemolysin, called the cytolysin, is important for pathogenesis in animal models of infection, and the cytolysin in combination with high-level gentamicin resistance is associated with a five-fold increase in risk of death in human bacteremia patients. A plasmid-encoded adhesin called "aggregation substance" is also important for virulence in animal models of infection.
E. faecalis is resistant to many commonly used antimicrobial agents. Resistance to vancomycin in E. faecalis is becoming more common. Treatment options for vancomycin-resistant E. faecalis include nitrofurantoin, linezolid, and daptomycin, although ampicillin is preferred if the bacteria are susceptible. Quinupristin/dalfopristin can be used to treat Enterococcus faecium but not E. faecalis. In root-canal treatments, NaOCl and chlorhexidine are used to fight E. faecalis before isolating the canal. However, recent studies determined that NaOCl or CHX showed low ability to eliminate E. faecalis.
Development of antibiotic resistance
Combined drug therapies
According to one study combined drug therapy has shown some efficacy in cases of severe infections against susceptible strains of E. faecalis. Ampicillin- and vancomycin-sensitive E. faecalis strains can be treated by gentamicin and ampicillin antibiotics. A less nephrotoxic combination of ampicillin and ceftriaxone may be used alternatively for ampicillin-susceptible E. faecalis. Daptomycin or linezolid may also show efficacy in case ampicillin and vancomycin resistance. A combination of penicillin and streptomycin therapy was used in the past.
Survival and virulence factors
Endures prolonged periods of nutritional deprivation
Activates the host protease plasminogen in a fashion that increases local tissue destruction
Historical
Prior to 1984, enterococci were members of the genus Streptococcus; thus, E. faecalis was known as Streptococcus faecalis. In 2013, a combination of cold denaturation and NMR spectroscopy was used to show detailed insights into the unfolding of the E. faecalis homodimeric repressor protein CylR2.
s play important roles in many cellular processes; 11 small RNAs have been experimentally characterised in E. faecalis V583 and detected in various growth phases. Five of them have been shown to be involved in stress response and virulence. A genome-wide sRNA study suggested that some sRNAs are linked to the antibiotic resistance and stress response in another Enteroccocus: E. faecium.
