Vancomycin-Resistant Enterococcus faecium (VREfm)-Introduction, Detection Methods, and Keynotes

Introduction of Vancomycin-Resistant Enterococcus faecium (VREfm)

Enterococcus faecium is a gram-positive, facultative anaerobic coccus that is part of the normal gastrointestinal flora but can cause nosocomial infections such as bloodstream infections, urinary tract infections, and intra-abdominal abscesses.

Vancomycin-resistant Enterococcus faecium (VREfm) is defined as an isolate that harbors van genes (vanA, vanB) that confer high-level resistance to vancomycin. This antibiotic binds to the D-Ala-D-Ala termini in bacterial cell wall precursors.

Detection Methods of Vancomycin-Resistant Enterococcus faecium (VREfm)

Method	Details
Disk Diffusion (Not preferred)	Poor correlation with MIC; not reliable alone for vancomycin resistance
Vancomycin MIC Testing	Gold standard: via broth microdilution or E-test
Chromogenic VRE Agar	Selective and differential; colonies show characteristic color (e.g., purple or blue)
VITEK 2 / Phoenix / MicroScan	Automated identification and susceptibility system
PCR for van genes (vanA, vanB)	Confirms presence of vancomycin resistance genes
Latex Agglutination (rare)	For detecting VanA/VanB antigens directly (less common)

Keynotes

1. VREfm is a major nosocomial pathogen, especially in ICUs, transplant units, and oncology wards.
2. Resistance is acquired, primarily via vanA or vanB genes on transposons or plasmids.
3. VanA confers high-level resistance to vancomycin and teicoplanin, while vanB gives variable vancomycin resistance but teicoplanin susceptibility.
4. Colonization (especially in the gut) can precede infection and facilitate nosocomial spread.
5. Hand hygiene and contact precautions are critical for preventing VRE outbreaks.
6. Routine screening of high-risk patients (e.g., rectal swab on chromogenic agar or PCR) is recommended in outbreak settings.
7. Linezolid, daptomycin, or tigecycline are therapeutic alternatives in VRE infections.
8. VRE is resistant to many antibiotics besides vancomycin (e.g., aminoglycosides, β-lactams).
9. E. faecalis is less frequently VRE; E. faecium is more likely to be multidrug-resistant.
10. Always confirm high MICs (>32 µg/mL) with molecular methods in critical infections.

Further Readings

1. https://pubmed.ncbi.nlm.nih.gov/31329096/
2. https://www.sciencedirect.com/science/article/pii/S0196655312001824
3. https://www.sciencedirect.com/science/article/pii/S0196655312001824
4. https://www.nature.com/articles/s41564-025-01958-0
5. https://www.cdc.gov/vre/about/index.html
6. https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2013.00048/full
7. https://www.health.wa.gov.au/~/media/Corp/Documents/Health-for/Infectious-disease/HISWA/VRE-OD-2014.pdf
8. https://link.springer.com/article/10.1007/s10096-011-1412-x