Enterococcus faecalis: Introduction, Morphology, Pathogenicity, Lab Diagnosis, Treatment, Prevention, and Keynotes

Enterococcus faecalis- Introduction, Morphology, Pathogenicity, Lab Diagnosis, Treatment, Prevention, and Keynotes_

Introduction

Enterococcus faecalis, formerly known as Streptococcus faecalis, is a gram-positive bacterium that belongs to the Enterococcus genus. Here are some key points about E. faecalis:

  1. Taxonomy and Classification: Enterococcus faecalis is a species of bacteria classified within the phylum Firmicutes, class Bacilli, order Lactobacillales, and family Enterococcaceae. It is part of the normal intestinal microbiota of humans and animals.
  2. Morphology: It is a spherical or ovoid-shaped bacterium that appears as pairs or short chains under a microscope. It is gram-positive, meaning it retains the crystal violet stain during the Gram staining procedure.
  3. Habitat: E. faecalis is commonly found in the gastrointestinal tract of humans and animals, including mammals and birds. It can also be present in various environmental sources, such as soil, water, and food.
  4. Pathogenicity: While it is generally considered a commensal bacterium, meaning it has a mutually beneficial relationship with its host, it can also act as an opportunistic pathogen. It is associated with various infections, including urinary tract infections, endocarditis, wound infections, and intra-abdominal infections.
  5. Antibiotic Resistance: It  has the ability to acquire resistance to multiple antibiotics, including vancomycin, a last-resort antibiotic. This antibiotic resistance poses challenges in the treatment of infections caused by this bacterium.
  6. Biofilm Formation: It has the ability to form biofilms, which are complex communities of bacteria encased in a self-produced matrix. Biofilms provide protection against antibiotics and host immune responses, making infections difficult to treat.
  7. Virulence Factors: E.  faecalis possesses various virulence factors that contribute to its pathogenicity. These include surface adhesins, cytolysin production, biofilm-associated factors, and the ability to resist host immune defenses.
  8. Laboratory Diagnosis: It can be isolated and identified in the laboratory using selective and differential media, such as bile esculin agar. Further confirmation can be done through biochemical tests, such as the PYR test (pyrrolidonyl arylamidase).
  9. Treatment: The choice of antibiotic therapy for Enterococcus faecalis infections depends on the specific clinical scenario and the antibiotic susceptibility profile of the strain. Commonly used antibiotics include ampicillin, vancomycin, linezolid, and daptomycin, among others.
  10. Infection Control: Preventing and controlling Enterococcus faecalis infections involves strict adherence to infection control measures, such as proper hand hygiene, isolation precautions, and appropriate disinfection practices.

Morphology

Enterococcus faecalis is a gram-positive bacterium with a distinct morphology. Here are some key characteristics of E. faecalis morphology:

  1. Shape: It  appears as spherical or ovoid-shaped cells, typically arranged in pairs or short chains.
  2. Size: The average diameter of E. faecalis cells ranges from 0.6 to 1.0 micrometers.
  3. Gram Staining: It  is gram-positive, meaning it retains the crystal violet stain during the Gram staining procedure. It appears purple-blue under a microscope.
  4. Cell Wall: It has a peptidoglycan-rich cell wall, which contributes to its gram-positive staining. The cell wall provides structural support and protection to the bacterium.
  5. Capsule: It can produce a polysaccharide capsule, although this feature is not present in all strains. The capsule can enhance the bacterium’s resistance to phagocytosis by the host immune system.
  6. Motility: It is generally non-motile and lacks flagella, which are the whip-like appendages used for bacterial motility.
  7. Spore Formation: It does not form spores. Spores are dormant and highly resistant structures formed by some bacteria under unfavorable conditions.
  8. Arrangement: Its cells are often found in pairs (diplococci) or short chains (streptococci). This arrangement can be observed when examining the bacterium under a microscope.

Pathogenicity

Enterococcus faecalis is an opportunistic pathogen, meaning it can cause infections, particularly in individuals with compromised immune systems or underlying medical conditions. Here are some key points about the pathogenicity of E. faecalis:

  1. Infections: It is associated with various types of infections, including urinary tract infections (UTIs), bloodstream infections (bacteremia), endocarditis (infection of the heart valves), intra-abdominal infections, wound infections, and infections of the pelvic region.
  2. Biofilm Formation: It has the ability to form biofilms, which are complex communities of bacteria encased in a self-produced matrix. Biofilms provide protection against host immune responses and antibiotics, making infections difficult to treat.
  3. Antibiotic Resistance: It has a remarkable ability to acquire resistance to antibiotics. It is often intrinsically resistant to many commonly used antibiotics, and some strains have developed resistance to even last-resort antibiotics, such as vancomycin.
  4. Virulence Factors: E.  faecalis produces various virulence factors that contribute to its ability to cause infections. These include surface adhesins that help it attach to host tissues, cytolysin production that can cause damage to host cells, and biofilm-associated factors that promote the formation and persistence of biofilms.
  5. Host Defense Evasion: Enterococcus faecalis can evade host immune responses by resisting phagocytosis (engulfment by immune cells) and modulating the host immune system’s inflammatory response.
  6. Horizontal Gene Transfer: It has the capacity for horizontal gene transfer, allowing it to acquire genetic elements, such as plasmids or transposons, that can carry antibiotic resistance genes. This contributes to the spread of antibiotic resistance among bacterial populations.
  7. Nosocomial Infections: It is frequently implicated in healthcare-associated infections, particularly in settings such as hospitals and long-term care facilities. These infections are often associated with invasive procedures, indwelling medical devices, and prolonged antibiotic use.
  8. Community-Acquired Infections: While less common, E. faecalis can also cause infections in the community, especially in individuals with underlying health conditions or compromised immune systems.

Lab Diagnosis

  • The laboratory diagnosis of Enterococcus faecalis involves several methods to isolate and identify the bacterium. Here are the key steps in the lab diagnosis of E. faecalis:
  1. Sample Collection: Clinical specimens, such as urine, blood, wound swabs, or other relevant body fluids, are collected from the patient suspected of having an Enterococcus faecalis infection.
  2. Sample Processing: The collected specimen is processed in the laboratory to isolate the bacteria. This may involve techniques such as culture, centrifugation, or filtration, depending on the type of specimen.
  3. Culture: The specimen is streaked onto appropriate culture media, such as blood agar or selective media like bile esculin agar. Enterococcus faecalis grows well on media containing bile esculin, which turns dark brown or black due to the hydrolysis of esculin by the bacterium.
  4. Colony Morphology: After incubation, colonies of Enterococcus faecalis appear as small, gray-white or cream-colored colonies on agar plates. The colonies are typically round, smooth, and may exhibit a narrow zone of beta-hemolysis on blood agar.
  5. Gram Staining: A Gram stain is performed on isolated colonies to confirm the gram-positive nature of Enterococcus faecalis. The bacterium will retain the crystal violet stain, appearing purple under a microscope.
  6. Biochemical Tests: Several biochemical tests are conducted to further identify Enterococcus faecalis. These tests may include catalase test (negative), oxidase test (negative), and the bile esculin hydrolysis test (positive).
  7. Confirmatory Tests: To confirm the identification of Enterococcus faecalis, additional tests can be performed. These may include the use of commercial identification kits, automated systems, or molecular methods like polymerase chain reaction (PCR).
  8. Antimicrobial Susceptibility Testing: The susceptibility of Enterococcus faecalis to different antibiotics is determined using methods like disk diffusion or automated systems. This helps guide appropriate antibiotic treatment.

Treatment

The treatment of Enterococcus faecalis infections depends on several factors, including the site and severity of infection, the patient’s overall health, and the antimicrobial susceptibility of the specific strain. Here are some key points regarding the treatment of E. faecalis infections:

  1. Antibiotic Therapy: E. faecalis is often resistant to multiple antibiotics, including some commonly used ones. However, many strains remain susceptible to certain antibiotics. The choice of antibiotics may include:
    • Ampicillin or amoxicillin: These are often the drugs of choice for susceptible strains.
    • Vancomycin: It is reserved for serious infections or when the strain is resistant to ampicillin.
    • Linezolid: It is an alternative for vancomycin-resistant strains or when other options are limited.
    • Daptomycin: It is effective against many strains of Enterococcus faecalis.
    • Nitrofurantoin: It is often used for urinary tract infections caused by susceptible strains.
  2. Combination Therapy: In some cases, combination therapy with two or more antibiotics may be necessary, especially for severe infections or when the strain is resistant to multiple drugs. The choice of combination therapy depends on the specific circumstances and the antimicrobial susceptibility profile.
  3. Antimicrobial Resistance: Enterococcus faecalis has a propensity for developing resistance to antibiotics. If the strain is resistant to commonly used drugs, susceptibility testing can guide the selection of alternative antibiotics. In severe cases, infectious disease specialists may be consulted for further guidance.
  4. Duration of Treatment: The duration of antibiotic treatment depends on the type and severity of the infection. It may range from a few days for uncomplicated urinary tract infections to several weeks for more severe infections, such as endocarditis.
  5. Source Control: In some cases, surgical intervention or drainage may be necessary to control the source of infection, such as abscesses or infected devices.
  6. Infection Prevention: In healthcare settings, infection prevention measures, such as hand hygiene, proper disinfection practices, and the appropriate use of antibiotics, are crucial in reducing the spread of Enterococcus faecalis infections.

Prevention

Preventing Enterococcus faecalis infections involves implementing measures to reduce the transmission of the bacterium and minimize the risk of infection. Here are some key points regarding the prevention of Enterococcus faecalis:

  1. Infection Control Practices: In healthcare settings, strict adherence to infection control protocols is crucial to prevent the spread of Enterococcus faecalis. This includes practices such as proper hand hygiene, wearing appropriate personal protective equipment, and implementing standard precautions for patient care.
  2. Environmental Cleaning: Regular and thorough cleaning and disinfection of patient care areas, medical equipment, and frequently touched surfaces can help reduce the environmental contamination and transmission of Enterococcus faecalis.
  3. Antimicrobial Stewardship: Responsible use of antibiotics is essential to prevent the development and spread of antibiotic-resistant strains of Enterococcus faecalis. Healthcare facilities should implement antimicrobial stewardship programs to promote appropriate antibiotic use, including optimizing dosing, duration, and selection of antibiotics.
  4. Hand Hygiene: Proper hand hygiene is crucial in preventing the transmission of Enterococcus faecalis. Healthcare workers should follow recommended hand hygiene practices, including washing hands with soap and water or using alcohol-based hand sanitizers, especially before and after patient contact.
  5. Patient Isolation: In healthcare settings, patients colonized or infected with Enterococcus faecalis may be placed under contact precautions, which may include isolation in a private room and the use of gloves and gowns by healthcare personnel during patient care.
  6. Urinary Catheter Care: Urinary tract infections caused by Enterococcus faecalis can be prevented by implementing proper insertion and maintenance techniques for urinary catheters. Avoiding unnecessary catheterization and early removal of catheters when no longer needed can help reduce the risk of infection.
  7. Proper Food Handling: Enterococcus faecalis can be present in food, particularly contaminated meat and dairy products. Practicing safe food handling, including proper cooking, storage, and hygiene practices in food preparation, can help prevent foodborne transmission.
  8. Personal Hygiene: Maintaining good personal hygiene, such as regular handwashing, especially after using the restroom, can reduce the risk of Enterococcus faecalis transmission.

Keynotes

  • Enterococcus faecalis is a Gram-positive bacterium that commonly inhabits the gastrointestinal tract of humans and animals.
  • It is a facultative anaerobe, meaning it can grow in the presence or absence of oxygen.
  • It is a leading cause of healthcare-associated infections, particularly urinary tract infections (UTIs), bloodstream infections, and surgical site infections.
  • It can also cause community-acquired infections, especially in individuals with underlying health conditions or compromised immune systems.
  • E. faecalis is known for its ability to develop resistance to multiple antibiotics, including vancomycin, which is considered a last-resort antibiotic.
  • It has the capacity to form biofilms, which contribute to its persistence and resistance to antibiotics.
  • The bacterium produces various virulence factors, including adhesins, cytolysin, and gelatinase, which help it colonize and cause infections in different host tissues.
  • Enterococcus faecalis is often transmitted through person-to-person contact or through contaminated healthcare equipment and surfaces.
  • In addition to causing infections, Enterococcus faecalis can also be a source of endocarditis, particularly in individuals with preexisting heart conditions.
  • The diagnosis of Enterococcus faecalis infections is typically performed through laboratory tests, including culture and identification of the bacterium.
  • Treatment of Enterococcus faecalis infections can be challenging due to its intrinsic and acquired antibiotic resistance. The choice of antibiotics depends on the site and severity of infection and the susceptibility profile of the specific strain.
  • Preventive measures, such as infection control practices, antimicrobial stewardship, hand hygiene, and proper food handling, play a crucial role in reducing the transmission and incidence of Enterococcus faecalis infections.

Further Readings

  1. Murray, B. E. (1990). The life and times of the Enterococcus. Clinical microbiology reviews, 3(1), 46-65.
  2. Hidron, A. I., Edwards, J. R., Patel, J., Horan, T. C., Sievert, D. M., Pollock, D. A., … & Fridkin, S. K. (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 & Hospital Epidemiology, 29(11), 996-1011.
  3. Arias, C. A., & Murray, B. E. (2012). The rise of the Enterococcus: beyond vancomycin resistance. Nature Reviews Microbiology, 10(4), 266-278.
  4. Fisher, K., & Phillips, C. (2009). The ecology, epidemiology and virulence of Enterococcus. Microbiology, 155(6), 1749-1757.
  5. Lebreton, F., van Schaik, W., & Manson McGuire, A. (2013). Emergence of epidemic multidrug-resistant Enterococcus faecium from animal and commensal strains. MBio, 4(4), e00534-13.
  6. Sava, I. G., Heikens, E., Huebner, J., & Pathak, A. (2010). Rapid identification and differentiation of clinically relevant Enterococcus species using a multiplex PCR-based reverse line blot hybridization assay. BMC microbiology, 10(1), 1-10.
  7. Kafil, H. S., & Asgharzadeh, M. (2014). Vancomycin-resistant enterococci: mechanisms and clinical observations. Clinical microbiology and infection, 20(5), 418-425.
  8. Toledo-Arana, A., Valle, J., Solano, C., Arrizubieta, M. J., Cucarella, C., Lamata, M., … & Lasa, I. (2001). The enterococcal surface protein, Esp, is involved in Enterococcus faecalis biofilm formation. Applied and environmental microbiology, 67(10), 4538-4545.
  9. Shankar, N., Baghdayan, A. S., & Gilmore, M. S. (2002). Modulation of virulence within a pathogenicity island in vancomycin-resistant Enterococcus faecalis. Nature, 417(6890), 746-750.
  10. Palmer, K. L., Godfrey, P., Griggs, A., Kos, V. N., Zucker, J., & Desjardins, C. (2012). Comparative genomics of enterococci: variation in Enterococcus faecalis, clade structure in E. faecium, and defining characteristics of E. gallinarum and E. casseliflavus. mBio, 3(1), e00318-11.
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