(Andrewes and Horder, 1906) Schleifer and Kilpper-Bälz, 1984
Enterococcus faecalis – formerly classified as part of the group D Streptococcus system – is a Gram-positive, commensalbacterium inhabiting the gastrointestinal tracts of humans.[1][2] Like other species in the genusEnterococcus, 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.[3] As an opportunistic pathogen, E. faecalis can cause life-threatening infections, especially in the nosocomial (hospital) environment, where the naturally high levels of antibiotic resistance found in E. faecalis contribute to its pathogenicity.[2][verification needed]E. faecalis has been frequently found in reinfected, root canal-treated teeth in prevalence values ranging from 30% to 90% of the cases.[4] Re-infected root canal-treated teeth are about nine times more likely to harbor E. faecalis than cases of primary infections.[5]
E. faecalis is found in most healthy individuals, but can cause endocarditis and sepsis, urinary tract infections (UTIs), meningitis, and other infections in humans.[7][8] 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.[9][10][11]Aplasmid-encoded adhesin[12] called "aggregation substance" is also important for virulence in animal models of infection.[10][13]
E. faecalis is usually resistant to many commonly used antimicrobial agents (aminoglycosides, aztreonam and quinolones.[15] The resistance is mediated by the presence of multiple genes related to drug resistance in the chromosome or plasmid.[3]
In root-canal treatments, NaOCl and chlorhexidine (CHX) 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.[20]
According to one study combined drug therapy has shown some efficacy in cases of severe infections (e.g. heart valves infections) against susceptible strains of E. faecalis. Ampicillin- and vancomycin-sensitive E. faecalis (lacking high-level resistance to aminoglycosides) strains can be treated by gentamicin and ampicillin antibiotics. A less nephrotoxic combination of ampicillin and ceftriaxone (even though E. faecalis is resistant to cephalosporins, ceftriaxone is working synergistically with ampicillin) may be used alternatively for ampicillin-susceptible E. faecalis.[21]
Daptomycinorlinezolid may also show efficacy in case ampicillin and vancomycin resistance.[21]
Produces extracellular superoxide under selected growth conditions that can generate chromosomal instability in mammalian cells[22][23]
Resists intracanal medicaments (e.g. calcium hydroxide), although a study proposes elimination from root canals after using a mixture of a tetracycline isomer, an acid, and a detergent[24]
Maintains pH homeostasis
Properties of dentin lessen the effect of calcium hydroxide
In human blood, E. faecalis is subjected to conditions that damage its DNA, but this damage can be tolerated by the use of DNA repair processes.[26] This damage tolerance depends, in part, on the two protein complex RexAB, encoded by the E. faecalis genome, that is employed in the recombinational repair of DNA double-strand breaks.[26]
Prior to 1984, enterococci were members of the genus Streptococcus; thus, E. faecalis was known as Streptococcus faecalis.[27]
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.[28]
Bacterial small RNAs play important roles in many cellular processes; 11 small RNAs have been experimentally characterised in E. faecalis V583 and detected in various growth phases.[31] Five of them have been shown to be involved in stress response and virulence.[32]
A genome-wide sRNA study suggested that some sRNAs are linked to the antibiotic resistance and stress response in another Enteroccocus: E. faecium.[33]
Because E. faecalis is a common fecal bacterium in humans, recreational water facilities (such as swimming pools and beaches that allow visitors to swim in the ocean) often measure the concentrations of E. faecalis to assess the quality of their water. The higher the concentration, the worse the quality of the water. The practice of using E. faecalis as a quality indicator is recommended by the World Health Organization (WHO) as well as many developed countries after multiple studies have reported that higher concentrations of E. faecalis correlate to greater percentages of swimmer illness. This correlation exists in both freshwater and marine environments, so measuring E. faecalis concentrations to determine water quality applies to all recreational waters. However, the correlation does not imply that E. faecalis is the ultimate cause of swimmer illnesses. One alternative explanation is that higher levels of E. faecalis correspond to higher levels of human viruses, which cause sickness in swimmers. Although this claim may sound plausible, there is currently little evidence that establishes the link between E. faecalis and human virus (or other pathogens) levels. Thus, despite the strong correlation between E. faecalis and water quality, more research is needed to determine the causal relationship of this correlation.[34]
For recreational waters near or at beaches, E. faecalis can come from multiple sources, such as the sand and human bodies. Determining the sources of E. faecalis is crucial for controlling water contamination, though often the sources are non-point (for example, human bathers). As such, one study looked at how much E. faecalis is shed from bathers at the beach. The first group of participants immersed themselves in a large pool with marine water for 4 cycles of 15 minutes, both with and without contacting sand beforehand. The result shows a decrease in E. faecalis levels for each cycle, suggesting that people shed the most bacteria when they first get into a pool. The second group of participants entered small, individual pools after contact with beach sand, and researchers collected data on how much E. faecalis in the pool came from the sand brought by the participants and how much came from the participants’ shedding. The result shows that E. faecalis from the sand is very small compared to that from human shedding. Although this result may not apply to all sand types, a tentative conclusion is that human shedding is a major non-point sourceofE. faecalis in recreational waters.[35]
^Molander A, Reit C, Dahlén G, Kvist T (January 1998). "Microbiological status of root-filled teeth with apical periodontitis". International Endodontic Journal. 31 (1): 1–7. doi:10.1046/j.1365-2591.1998.t01-1-00111.x. PMID9823122.
^Rôças IN, Siqueira JF, Santos KR (May 2004). "Association of Enterococcus faecalis with different forms of periradicular diseases". Journal of Endodontics. 30 (5): 315–320. doi:10.1097/00004770-200405000-00004. PMID15107642.
^Hidron AI, Edwards JR, Patel J, Horan TC, Sievert DM, Pollock DA, et al. (November 2008). "NHSN annual update: antimicrobial-resistant pathogens associated with healthcare-associated infections: annual summary of data reported to the National Healthcare Safety Network at the Centers for Disease Control and Prevention, 2006-2007". Infection Control and Hospital Epidemiology. 29 (11): 996–1011. doi:10.1086/591861. PMID18947320. S2CID205988392.
^ abcdSingh H, Das S, Yadav J, Srivastava VK, Jyoti A, Kaushik S (October 2019). "In search of novel protein drug targets for treatment of Enterococcus faecalis infections". Chemical Biology & Drug Design. 94 (4). Wiley: 1721–1739. doi:10.1111/cbdd.13582. PMID31260188. S2CID195756723.
^Huycke MM, Moore D, Joyce W, Wise P, Shepard L, Kotake Y, et al. (November 2001). "Extracellular superoxide production by Enterococcus faecalis requires demethylmenaquinone and is attenuated by functional terminal quinol oxidases". Molecular Microbiology. 42 (3): 729–740. doi:10.1046/j.1365-2958.2001.02638.x. PMID11722738. S2CID25075356.
^Shabahang S, Pouresmail M, Torabinejad M (July 2003). "In vitro antimicrobial efficacy of MTAD and sodium hypochlorite". Journal of Endodontics. 29 (7): 450–452. doi:10.1097/00004770-200307000-00006. PMID12877261.
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