universe84a

Introduction

Enterococcus faecium is a Gram-positive bacterium that belongs to the genus Enterococcus. It is a facultative anaerobe, meaning it can grow both in the presence and absence of oxygen. It  is commonly found in the gastrointestinal tract of humans and animals as part of the normal microbiota. However, it can also be associated with various healthcare-associated infections and has emerged as a significant nosocomial pathogen.

Here are some key points about Enterococcus faecium:

1. Clinical Significance: Enterococcus faecium is known for its ability to cause a range of infections, including urinary tract infections, bloodstream infections (bacteremia), surgical site infections, endocarditis, and intra-abdominal infections. It is often associated with infections in hospitalized patients, especially those with weakened immune systems or undergoing invasive procedures.
2. Antibiotic Resistance: It  has gained attention due to its high level of antibiotic resistance. It is often resistant to multiple antibiotics, including vancomycin, which is a crucial antibiotic for treating Gram-positive infections. Vancomycin-resistant Enterococcus faecium (VRE) strains have become a significant concern in healthcare settings and pose challenges for treatment.
3. Nosocomial Transmission: It can spread within healthcare facilities, leading to outbreaks. It is known for its ability to persist in the hospital environment and colonize patients for an extended period. Transmission can occur through direct contact with contaminated surfaces, healthcare workers’ hands, or through patient-to-patient contact.
4. Biofilm Formation: It has the ability to form biofilms, which are complex communities of bacteria encased in a protective matrix. Biofilms contribute to the organism’s resistance to antibiotics and disinfectants, making infections more challenging to treat.
5. Genetic Exchange: It possesses mechanisms for horizontal gene transfer, allowing it to acquire antibiotic resistance genes and other virulence factors. This genetic plasticity contributes to the evolution and persistence of antimicrobial-resistant strains.
6. Diagnosis and Treatment: Diagnosis of Enterococcus faecium infections typically involves culturing the organism from clinical specimens such as blood, urine, or wound swabs. Treatment can be challenging due to the high levels of antibiotic resistance. In some cases, combination therapy or the use of newer agents may be necessary to effectively manage infections caused by this organism.

It’s important to note that while Enterococcus faecium is often associated with healthcare-associated infections, it is not typically a primary pathogen in healthy individuals. However, in healthcare settings or individuals with compromised immunity, it can pose a significant risk. Proper infection control measures, including hand hygiene, environmental cleaning, and prudent antibiotic use, are crucial in preventing the spread of E. faecium and managing infections.

Morphology

Enterococcus faecium exhibits a specific morphology that can be observed under a microscope. Here are the key features of its  morphology:

1. Cell Shape: It is a spherical bacterium that typically appears as cocci, which are round or oval-shaped cells. The cells are generally arranged in pairs (diplococci) or short chains (streptococci) when observed under a microscope.
2. Gram Staining: It is a Gram-positive bacterium. This means that it retains the crystal violet stain during the Gram staining procedure and appears purple under a microscope. The Gram-positive nature is attributed to the thick peptidoglycan layer present in the cell wall.
3. Cell Size: The size of its cells can vary, but they generally range between 0.5 to 1.0 micrometers in diameter. These dimensions may vary slightly depending on growth conditions and other factors.
4. Lack of Flagella: E. faecium is generally non-motile and does not possess flagella, the whip-like appendages used for bacterial motility.
5. Capsule: Some strains of  it may produce a polysaccharide capsule surrounding the cell. The capsule can contribute to the bacterium’s virulence and ability to evade the host immune response. However, not all strains of Enterococcus faecium possess capsules.

Pathogenicity

Enterococcus faecium can exhibit pathogenicity, particularly in certain clinical settings and individuals with compromised immune systems. While it is considered a normal member of the gastrointestinal microbiota, it can cause opportunistic infections and has gained attention as a healthcare-associated pathogen. Here are key aspects of the pathogenicity of E. faecium:

1. Antibiotic Resistance: It is well-known for its ability to develop resistance to multiple antibiotics. This resistance can limit treatment options and contribute to persistent infections. Vancomycin-resistant Enterococcus faecium (VRE) strains are particularly concerning, as they exhibit resistance to one of the most important antibiotics used to treat Gram-positive infections.
2. Healthcare-Associated Infections: It is frequently associated with healthcare settings, including hospitals and long-term care facilities. It can cause various infections, such as urinary tract infections, bloodstream infections (bacteremia), surgical site infections, endocarditis, and intra-abdominal infections. Invasive procedures, indwelling medical devices, and prolonged antibiotic use increase the risk of Enterococcus faecium infections.
3. Biofilm Formation: It has the ability to form biofilms, which are complex communities of bacteria embedded in a matrix. Biofilms can develop on various surfaces, including medical devices like catheters and prosthetic heart valves. The biofilm’s protective nature makes it difficult for antibiotics and the immune system to eliminate the infection, leading to chronic or recurrent infections.
4. Virulence Factors: It possesses various virulence factors that contribute to its pathogenicity. Some of these factors include adhesins, which allow the bacterium to attach to host tissues, and enzymes such as gelatinase and hyaluronidase, which facilitate tissue invasion and destruction. Enterococcus faecium also produces toxins, including cytolysin, which may contribute to host cell damage.
5. Horizontal Gene Transfer: It has the ability to acquire antibiotic resistance genes and other virulence determinants through horizontal gene transfer. This genetic plasticity enables the bacterium to rapidly adapt to new environments and develop increased resistance to antibiotics, further enhancing its pathogenic potential.

Lab Diagnosis

The laboratory diagnosis of Enterococcus faecium infections involves several methods to isolate and identify the bacterium. Here are the key steps involved in the lab diagnosis of E. faecium:

1. Specimen Collection: Clinical specimens, such as blood, urine, wound swabs, or other relevant samples, are collected from the patient suspected of having an Enterococcus faecium infection. Proper collection techniques are followed to ensure the accuracy of the results.
2. Culture and Isolation: The collected specimens are streaked onto selective and differential agar media, such as blood agar or chromogenic agar. It is a facultative anaerobe and can grow under both aerobic and anaerobic conditions. The agar plates are incubated at an appropriate temperature, typically around 35-37°C, for 24 to 48 hours.
3. Colony Morphology: Its colonies appear as small to medium-sized, smooth, and grayish-white colonies on agar plates. Further identification tests are necessary to confirm the presence of Enterococcus faecium.
4. Gram Staining: Gram staining is performed to determine the Gram reaction of the isolated colonies. It is Gram-positive and appears as purple cocci under the microscope.
5. Biochemical Tests: Several biochemical tests are conducted to identify E.  faecium and distinguish it from other bacteria. These tests include catalase test (negative), oxidase test (negative), bile esculin hydrolysis (positive), and growth in 6.5% NaCl (positive). Enterococcus faecium is known to be able to grow in high salt concentrations.
6. Confirmation of Identification: Once the preliminary tests suggest the presence of Enterococcus faecium, further confirmation can be achieved using more specific methods. These may include molecular techniques such as polymerase chain reaction (PCR) targeting specific genetic markers or genes associated with Enterococcus faecium.
7. Antimicrobial Susceptibility Testing: As Enterococcus faecium is known for its high level of antibiotic resistance, it is essential to perform antimicrobial susceptibility testing on the isolated strain. This helps guide appropriate antibiotic treatment and monitor the emergence of resistant strains, especially vancomycin resistance (VRE).
8. Reporting and Interpretation: The laboratory findings, including the identification of E. faecium and its antibiotic susceptibility profile, are reported to the healthcare provider to guide patient management and treatment decisions.

Treatment

The treatment of Enterococcus faecium infections can be challenging due to the bacterium’s high levels of antibiotic resistance. The choice of treatment depends on various factors, including the site of infection, severity, patient factors, and antibiotic susceptibility profile of the specific strain. Here are some general considerations for the treatment of E. faecium infections:

1. Antibiotic Susceptibility Testing: It is crucial to perform antimicrobial susceptibility testing to determine the antibiotic susceptibility profile of the specific Enterococcus faecium strain. This helps guide appropriate antibiotic selection.
2. Combination Therapy: In severe infections or those caused by multidrug-resistant strains, combination therapy with multiple antibiotics may be considered. Common combinations include ampicillin or vancomycin with an aminoglycoside (e.g., gentamicin or streptomycin). This approach aims to enhance the effectiveness of treatment and overcome resistance mechanisms.
3. Ampicillin: Ampicillin, a beta-lactam antibiotic, is generally active against Enterococcus faecium. However, many strains have acquired resistance to ampicillin through the production of beta-lactamase enzymes. Ampicillin is often used in combination with an aminoglycoside or another antibiotic.
4. Vancomycin: Vancomycin is an important antibiotic for the treatment of Enterococcus faecium infections, particularly if the strain is susceptible. However, the emergence of vancomycin-resistant Enterococcus faecium (VRE) limits the effectiveness of vancomycin in some cases. If the strain is VRE, alternative treatment options need to be considered.
5. Linezolid: Linezolid is an oxazolidinone antibiotic with activity against multidrug-resistant Enterococcus faecium, including VRE. It is often used as an alternative treatment option when other agents are not effective or in the presence of resistance.
6. Daptomycin: Daptomycin, a lipopeptide antibiotic, can be considered for the treatment of Enterococcus faecium infections, including those caused by VRE. It has demonstrated activity against certain resistant strains.
7. Other Agents: In some cases, alternative antibiotics such as tigecycline, quinupristin/dalfopristin, or combinations involving newer agents may be considered. However, their use should be based on susceptibility testing and expert consultation.
8. Infection Control Measures: In healthcare settings, strict infection control measures, such as hand hygiene, appropriate isolation precautions, and environmental cleaning, are essential to prevent the spread of Enterococcus faecium infections.

Prevention

Preventing the spread of Enterococcus faecium and reducing the risk of infection primarily involves implementing comprehensive infection control measures. Here are some key strategies for the prevention of Enterococcus faecium:

1. Hand Hygiene: Proper hand hygiene is critical in preventing the transmission of Enterococcus faecium. Healthcare workers should adhere to strict hand hygiene practices, including washing hands with soap and water or using alcohol-based hand sanitizers before and after patient contact.
2. Environmental Cleaning and Disinfection: Regular and thorough cleaning and disinfection of patient care areas, equipment, and frequently touched surfaces are essential to remove and kill Enterococcus faecium. Healthcare facilities should follow appropriate disinfection protocols and use effective disinfectants.
3. Contact Precautions: Patients infected or colonized with Enterococcus faecium should be placed on contact precautions. This includes using gloves and gowns when entering the patient’s room to prevent the spread of the bacterium to other patients or healthcare workers.
4. Antimicrobial Stewardship: Appropriate and judicious use of antibiotics is crucial in preventing the emergence and spread of antibiotic-resistant Enterococcus faecium. Implementing antimicrobial stewardship programs can help optimize antibiotic use, reduce unnecessary prescriptions, and minimize the development of resistance.
5. Surveillance and Screening: Active surveillance for Enterococcus faecium infections and colonization can help identify cases and implement control measures promptly. Screening high-risk patients, such as those in intensive care units or undergoing certain procedures, may be considered to identify asymptomatic carriers and prevent transmission.
6. Patient and Staff Education: Educating patients, visitors, and healthcare staff about the importance of infection control measures, including hand hygiene and proper use of personal protective equipment, can help raise awareness and promote compliance.
7. Cohorting and Isolation: When feasible, patients infected or colonized with Enterococcus faecium should be cohorted or isolated to minimize the risk of transmission to other patients.
8. Antibiotic Resistance Monitoring: Monitoring antibiotic resistance patterns and sharing data at the local, regional, and national levels can help identify emerging resistance trends and guide infection control practices and treatment strategies.

Keynotes

• Enterococcus faecium is a Gram-positive bacterium commonly found in the gastrointestinal tract of humans and animals.
• It is an opportunistic pathogen that can cause healthcare-associated infections, particularly in immunocompromised individuals.
• It is known for its ability to develop antibiotic resistance, including resistance to vancomycin, which has led to the emergence of vancomycin-resistant Enterococcus faecium (VRE).
• The bacterium can cause a range of infections, including urinary tract infections, bloodstream infections (bacteremia), surgical site infections, endocarditis, and intra-abdominal infections.
• It can form biofilms, which contribute to its ability to adhere to surfaces, resist antibiotics, and cause chronic or recurrent infections.
• The pathogenicity of Enterococcus faecium is attributed to various virulence factors, including adhesins, enzymes, and toxins.
• Laboratory diagnosis of Enterococcus faecium involves culture, Gram staining, biochemical tests, and confirmation through specific methods such as molecular techniques.
• Treatment of Enterococcus faecium infections can be challenging due to antibiotic resistance. Treatment options may include combinations of antibiotics, such as ampicillin with an aminoglycoside, or alternative agents like vancomycin, linezolid, or daptomycin.
• Prevention of Enterococcus faecium involves strict adherence to infection control measures, including hand hygiene, environmental cleaning, contact precautions, and antimicrobial stewardship.
• Surveillance, screening, patient education, and antimicrobial resistance monitoring are essential components of preventing the spread of Enterococcus faecium and controlling infections.
• Collaboration between healthcare providers, microbiologists, and infection control professionals is important in managing and preventing Enterococcus faecium infections.

Further Readings

1. Arias, C. A., & Murray, B. E. (2012). The rise of the Enterococcus: beyond vancomycin resistance. Nature Reviews Microbiology, 10(4), 266-278.
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. Lebreton, F., van Schaik, W., & Manson McGuire, A. (2017). Enterococcus faecium, an emerging nosocomial pathogen. FEMS Microbiology Reviews, 41(3), 430-449.
4. Nallapareddy, S. R., & Murray, B. E. (2008). Clinical isolates of Enterococcus faecium exhibit strain-specific collagen binding mediated by Acm, a new member of the MSCRAMM family. Molecular Microbiology, 68(3), 509-521.
5. Paganelli, F. L., Willems, R. J., & Leavis, H. L. (2012). Optimizing future treatment of enterococcal infections: attacking the biofilm? Trends in Microbiology, 20(1), 40-49.
6. Sava, I. G., Heikens, E., Huebner, J., & Pathirana, R. D. (2010). Harnessing pathogen-derived immunomodulatory molecules for therapeutic use–lessons from the genus Enterococcus. Frontiers in Microbiology, 1, 111.
7. Tedim, A. P., Ruiz-Garbajosa, P., Corander, J., Rodríguez, C. M., Canton, R., Willems, R. J., & Baquero, F. (2015). Population biology of intestinal Enterococcus isolates from hospitalized and nonhospitalized individuals in different age groups. Applied and Environmental Microbiology, 81(5), 1820-1831.