Enterococcus faecalis, alternately known as Streptococcus faecalis, belongs to the Group II of the enterococci family. It is a Gram-positive bacterium that survives in various environments, exhibiting stronger resistance to environmental conditions compared to other bacteria[1]. E. faecalis significantly contributes to hospital-acquired infections, particularly affecting immunocompromised individuals such as the elderly, infants, and those with weakened immune systems[2]. The infections associated with this bacterial species include bacteremia, endocarditis, urinary tract, intra-abdominal, meningitis, surgical site, and device-associated infections[3].
Although E. faecalis is a prime cause of hospital-acquired infections, it's also found in various foods like vegetables, dairy products, fish, and meats, possibly contributing to human transmission[4-6]. Several studies have demonstrated the transmission of E. faecalis from animals to humans through the consumption of contaminated food[7-9]. Despite being considered a relatively mild pathogen, E. faecalis is capable of forming biofilms and acquiring mobile genetic elements (MGEs) that confer drug resistance, notably to drugs like vancomycin, posing treatment challenges[3,10]. Moreover, due to intrinsic resistance mechanisms, the therapeutic options for Enterococcus infections are limited[10].
Diverse kinds of virulence factors have been reported to enhance the pathogenicity of E. faecalis strains by enabling the colonization and invasion of host tissue, translocation through epithelial cells, and evasion from the host's immune response. The major virulence factors associated with the pathogenicity of enterococci virulent strains include enterococcal surface proteins (Esp), hyaluronidase (Hyl) aggregation substance (AS), gelatinase (gelE), and cytolysin (Cyl)[11]. In addition to having a variety of virulence factors and resistance genes, E. faecalis is also highly proficient at exchanging and transmitting many of these genes through horizontal gene transfer[12].
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[1] Matle I, Atanda AC, Pierneef R, Magwedere K, Mafuna T. Resistome, mobilome, virulome analysis and phylogenomics of Enterococcus faecalis isolated from raw muscle foods of beef origin in Gauteng, South Africa. Genomics. 2023;115(6):110742.
[2] Krawczyk B, Wityk P, Gałęcka M, Michalik M. The Many Faces of Enterococcus spp.-Commensal, Probiotic and Opportunistic Pathogen. Microorganisms. 2021;9(9):1900.
[3] Chilambi GS, Nordstrom HR, Evans DR, et al. Genomic and phenotypic diversity of Enterococcus faecalis isolated from endophthalmitis. PLoS One. 2021;16(4):e0250084.
[4] Bondi M, Laukova A, de Niederhausern S, Messi P, Papadopoulou C, Economou V. Controversial Aspects Displayed by Enterococci: Probiotics or Pathogens?. Biomed Res Int. 2020;2020:9816185.
[5] Tamang MD, Moon DC, Kim SR, et al. Detection of novel oxazolidinone and phenicol resistance gene optrA in enterococcal isolates from food animals and animal carcasses. Vet Microbiol. 2017;201:252-256.
[6] Ben Braïek O, Smaoui S. Enterococci: Between Emerging Pathogens and Potential Probiotics. Biomed Res Int. 2019;2019:5938210.
[7] Gelsomino R, Vancanneyt M, Cogan TM, Condon S, Swings J. Source of enterococci in a farmhouse raw-milk cheese. Appl Environ Microbiol. 2002;68(7):3560-3565.
[8] Larsen J, Schønheyder HC, Lester CH, et al. Porcine-origin gentamicin-resistant Enterococcus faecalis in humans, Denmark. Emerg Infect Dis. 2010;16(4):682-684.
[9] Anderson AC, Jonas D, Huber I, et al. Enterococcus faecalis from Food, Clinical Specimens, and Oral Sites: Prevalence of Virulence Factors in Association with Biofilm Formation. Front Microbiol. 2016;6:1534.
[10] Aun E, Kisand V, Laht M, et al. Molecular Characterization of Enterococcus Isolates From Different Sources in Estonia Reveals Potential Transmission of Resistance Genes Among Different Reservoirs. Front Microbiol. 2021;12:601490.
[11] Kiruthiga A, Padmavathy K, Shabana P, Naveenkumar V, Gnanadesikan S, Malaiyan J. Improved detection of esp, hyl, asa1, gelE, cylA virulence genes among clinical isolates of Enterococci. BMC Res Notes. 2020;13(1):170.
[12] Akter T, Haque MN, Ehsan R, et al. Virulence and antibiotic-resistance genes in Enterococcus faecalis associated with streptococcosis disease in fish. Sci Rep. 2023;13(1):1551.