Enterococcus faecalis

Enterococcus faecalis – formerly classified as part of the group D "Streptococcus" system – is a Gram-positive, commensal bacterium 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. 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.
"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.
Physiology.
"E. faecalis" is a nonmotile microbe; it ferments glucose without gas production, and does not produce a catalase reaction with hydrogen peroxide. It produces a reduction of litmus milk, but does not liquefy gelatin. It shows consistent growth throughout nutrient broth which is consistent with being a facultative anaerobe. It catabolizes a variety of energy sources, including glycerol, lactate, malate, citrate, arginine, agmatine, and many keto acids. Enterococci survive very harsh environments, including extremely alkaline pH (9.6) and salt concentrations. They resist bile salts, detergents, heavy metals, ethanol, azide, and desiccation. They can grow in the range of 10 to 45 °C and survive at temperatures of 60 °C for 30 min.
Pathogenesis.
"E. faecalis" is found in most healthy individuals, but can cause endocarditis and sepsis, urinary tract infections (UTIs), 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.
Antibacterial resistance.
Multi drug resistance.
"E. faecalis" is usually resistant to many commonly used antimicrobial agents (aminoglycosides, aztreonam and quinolones. The resistance is mediated by the presence of multiple genes related to drug resistance in the chromosome or plasmid.
Resistance to vancomycin in "E. faecalis" is becoming more common. Treatment options for vancomycin-resistant "E. faecalis" include nitrofurantoin (in the case of uncomplicated UTIs), linezolid, quinupristin, tigecycline 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 (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".
Combined drug therapies.
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".
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.
Tedizolid, telavancin, dalbavancin, and oritavancin antibiotics are FDA approved as treatments against EF.
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.
Genome structure.
The "E. faecalis" genome consists of 3.22 million base pairs with 3,113 protein-coding genes.
Treatment research.
Glutamate racemase, hydroxymethylglutaryl-CoA synthase, diphosphomevalonate decarboxylase, topoisomerase DNA gyrase B, D-alanine—D-serine ligase, alanine racemase, phosphate acetyltransferase, NADH peroxidase,Phosphopantetheine adenylyltransferase (PPAT), acyl carrier protein, 3‐Dehydroquinate dehydratase and Deoxynucleotide triphosphate triphosphohydrolase are all potential molecules that may be used for treating EF infections.
Small RNA.
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. 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".