Enterococcus faecalis

◉ Classification and Nomenclature

Enterococcus faecalis belongs to the genus Enterococcus, in the family Enterococcaceae, order Lactobacillales, and class Bacilli.

E. faecalis was first isolated and identified in 1899 by the German microbiologist Fritz Schmalz. It was initially classified as Streptococcus faecalis due to its similarities with other streptococci.

In 1984, based on biochemical, genetic, and cell wall characteristics, the International Committee on Systematics of Prokaryotes proposed reclassifying the group Streptococcus faecalis into a distinct genus, Enterococcus.

◉ Epidemiology

Enterococci are commonly found in the human and animal digestive tract, often colonizing the skin and genitourinary pathways. Enterococcus faecalis is the predominant species within the genus, constituting 80 to 90% of clinical isolates.

These bacteria are opportunistic and ubiquitous, capable of surviving for several weeks in the hospital environment, especially on contaminated surfaces and laundry.

Despite being relatively low in virulence factors compared to other bacteria, the accumulation of resistance mechanisms and the increasing frequency of their isolation, particularly in nosocomial infections, have sparked renewed interest in this bacterial genus.

Infections with Enterococcus faecalis are more common in individuals with weakened immune systems, those suffering from chronic diseases, cancer, organ transplants, or invasive procedures. Elderly individuals, infants, and pregnant women are also more susceptible to E. faecalis infections.

Enterococci faecalis are transmitted through direct contact, via surfaces (able to survive up to 4 months on dry surfaces), as well as through water and contaminated food.

◉ Clinical Manifestations

The symptoms of an Enterococcus faecalis infection depend on the location and severity of the infection, as well as the person's immune status and underlying health conditions.

Some of the common clinical manifestations of E. faecalis infections are:

◉ 1- Urinary tract infections (UTIs)

Urinary infection by Enterococcus faecalis is more common in hospital settings, particularly if the patient is male, catheterized, or has received broad-spectrum antibiotic therapy.

The infection can be monobacterial or associated with other germs (Gram-negative bacteria), causing either colonization, asymptomatic bacteriuria, or typical urinary infections (pain, burning when urinating, polyuria, cloudy or bloody urine, etc.).

◉ 2- Endocarditis

This is an infection of the inner lining of the heart or heart valves. Enterococcus faecalis can cause endocarditis by entering the bloodstream through the digestive or genitourinary tract, during dental procedures, intravenous drug use, or other means.

Endocarditis is more common as the patient gets older or if there is pre-existing heart disease. It can cause fever, chills, fatigue, chest pain, shortness of breath, and a heart murmur.

◉ 3- Bacteremia

Enterococcus faecalis can cause bacteremia by contaminating a catheter, a dialysis port or spreading from a urinary, biliary, intra-abdominal or superficial site (the skin of a burn victim).

Bacteremias are often nosocomial with a severe prognosis, it can cause fever, chills, fatigue, headaches, rapid breathing and low blood pressure or even death.

◉ 4- Wound infections

They typically occur as a result of contamination of a wound, either through direct contact with the bacterium or from its spread from another infected site with Enterococcus faecalis.

These infections can manifest with symptoms such as localized pain, swelling, redness, and discharge. In more severe cases, systemic symptoms like fever, chills, and fatigue may also be present.

◉ 5- Meningitis

E. faecalis can cause meningitis by entering the bloodstream through a head injury, surgery, or other means. Meningitis can cause fever, headache, stiff neck, sensitivity to light, confusion, and seizures.

◉ Identification and Bacteriological Characters

Enterococcus faecalis can be identified by its cultural, biochemical, and molecular characteristics. Some of the methods used for identification include:

◉ 1- Direct examination

Under the microscope and after Gram staining, Enterococcus faecalis appears as oval or round Gram-positive cocci grouped in pairs or short chains.

◉ 2- Culture

Enterococcus faecalis grows easily on common culture media under normal atmospheric conditions, typically within 18 to 24 hours, at temperatures ranging from 10 to 45 °C.

E. faecalis produces small colonies (pinpoint colonies), smooth, gray, or whitish-gray in appearance, showing non-hemolytic (γ-hemolytic) characteristics, although some strains may be beta-hemolytic on blood agar.

They can also thrive in extreme conditions such as the presence of 6.5% NaCl, 40% bile salts, and at a pH of 9.5. These conditions are often used as diagnostic aids.

Bile-esculin-azide agar and CNA agar (Colistin Nalidixic Acid agar) are specific culture media that promote the growth of enterococci while inhibiting the growth of other bacteria.

◉ 3- Identification of the genus Enterococcus

◉ 4- Identification of the Enterococcus faecalis species and biochemical characterization

Identifying the species of enterococci isolated from severe infections is crucial for effective treatment and epidemiological monitoring.

Resistance to potassium tellurite is a key characteristic for the rapid identification of Enterococcus faecalis. Additionally, E. faecalis is characterized by the following:

For more complete biochemical identification, biochemical galleries such as Api 20 strep or bacteriological identification automates (MicroScan WalkAway plus System, ALFRED 60/AST.. ) can be used.

◉ 5- Molecular diagnosis

E. faecalis can be identified by using polymerase chain reaction (PCR) to amplify specific genes.

◉ 6- Antibiotic resistance profile

The antibiotic resistance profile can also help differentiate between different species of enterococci:

◉ Resistance

Enterococcus faecalis is known for its ability to resist many antibiotics, making it harder to treat. This bacterium has the capability to form biofilms, which are bacterial communities adhering to surfaces and shielded by a matrix of extracellular substances.

The biofilm formation serves as protection against host immune responses, rendering Enterococcus faecalis even more resilient to antibiotics and disinfectants.

Intrinsic resistance

Enterococcus faecalis is known for its intrinsic resistance to certain antibiotics, including oxacillin, penicillins, cephalosporins, monobactams, lincosamides, and streptogramin A (LSA phenotype). Additionally, it exhibits a low susceptibility to aminoglycosides due to the inefficient transport of these antibiotics across the cytoplasmic membrane.

Acquired resistance

Enterococcus faecalis can acquire resistance to antibiotics by various mechanisms: production of penicillinase, increased expression of low affinity PLP5, alteration of the molecular target (resistance to streptomycin), acquisition of Van genes (A, B, D ,E,G). The latter are responsible for resistance at variable levels to vancomycin and teicoplanin.

◉ Surveillance

Surveillance of Enterococcus faecalis is important to monitor the prevalence, incidence, and resistance profiles of this bacterium, which can cause infections in various parts of the body, especially in hospitalized patients.

Surveillance methods include laboratory testing, reporting and tracking of enterococcal isolates, and infection control measures, such as hand hygiene, environmental cleaning, and appropriate use of antibiotics.

◉ Conclusion

In conclusion, Enterococcus faecalis is a bacterium that demands attention and further investigation. By enhancing our knowledge and implementing comprehensive strategies, we can better combat the challenges posed by this pathogen and improve patient outcomes in healthcare settings.


  1. Viana, K. A., Filho, O. a. M., Dusse, L. M. S., Avelar, R. S., Avelar, D. M. V., Carvalho, B., Ribeiro, C. M. F., Antonelli, L. R. D. V., Teixeira, A., & Carvalho, M. D. G. (2014). Reticulocyte count: comparison among methods. Jornal Brasileiro De Patologia E Medicina Laboratorial, 50(5). https://doi.org/10.5935/1676-2444.20140037
  2. Uppal, V., Naseem, S., Bihana, I., Sachdeva, M. U. S., & Varma, N. (2020). Reticulocyte count and its parameters: comparison of automated analyzers, flow cytometry, and manual method. Journal of Hematopathology, 13(2), 89–96. https://doi.org/10.1007/s12308-020-00395-8
  3. Dg, D. (n.d.). How to Count Reticulocytes (Manual Method). BIOSCIENCE. https://www.bioscience.com.pk/topics/cell-biology/item/146-how-to-count-reticulocytes
  4. Poyart, C., Quesnes, G., & Trieu‐Cuot, P. (2000). Sequencing the gene encoding Manganese-Dependent superoxide dismutase for rapid species identification of enterococci. Journal of Clinical Microbiology, 38(1), 415–418. https://doi.org/10.1128/jcm.38.1.415-418.2000
  5. Masson, E. (n.d.). Entérocoques. EM-Consulte. https://www.em-consulte.com/article/60991/enterocoques
  6. Laboratory surveillance of Enterococcus spp. bacteraemia in England: 2020
  7. Hollenbeck, B., & Rice, L. B. (2012). Intrinsic and acquired resistance mechanisms in enterococcus. Virulence, 3(5), 421–569. https://doi.org/10.4161/viru.21282
  8. Alia Codelia-Anjum et al - Enterococcal Urinary Tract Infections: A Review of the Pathogenicity, Epidemiology, and Treatment
  9. Miller, W. R., Munita, J. M., & Arias, C. A. (2014). Mechanisms of antibiotic resistance in enterococci. Expert Review of Anti-infective Therapy, 12(10), 1221–1236. https://doi.org/10.1586/14787210.2014.956092
  10. García-Solache, M., & Rice, L. B. (2019). The Enterococcus: a Model of Adaptability to Its Environment. Clinical Microbiology Reviews, 32(2). https://doi.org/10.1128/cmr.00058-18
  11. Actor, J. K. (2012). Clinical bacteriology. In Elsevier eBooks (pp. 105–120). https://doi.org/10.1016/b978-0-323-07447-6.00012-0
  12. Clinisciences. (n.d.). Columbia CNA Agar - Selective solid media for microbiology Clinisciences. https://www.clinisciences.com/en/buy/cat-columbia-cna-agar-selective-solid-5535.html