Энтерококк фекалис: характеристики, патогенность и устойчивость к антибиотикам.

Species of bacterium

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. Re infected root canal treated teeth are about nine times more likely to harbor E. faecalis than cases of primary infections.

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. 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 contains a tyrosine decarboxylase enzyme capable of decarboxylating L DOPA, a crucial drug in the treatment of Parkinson's disease. If L DOPA is decarboxylated in the gut microbiome, it cannot pass through the blood brain barrier and be decarboxylated in the brain to become dopamine.

E. faecalis is usually resistant to many commonly used antimicrobial agents (aminoglycosides, aztreonam and quinolones. Treatment options for vancomycin resistant E. faecalis include nitrofurantoin (in the case of uncomplicated UTIs), linezolid, quinupristin, tigecycline Quinupristin/dalfopristin can be used to treat Enterococcus faecium but not E. faecalis.

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.

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. 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. 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.

The E. faecalis genome consists of 3.22 million base pairs with 3,113 protein coding genes.

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.

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.

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.

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 source of E. faecalis in recreational waters.