Introduction of Vancomycin-Resistant Enterococcus faecium (VREfm)
Table of Contents
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
- VREfm is a major nosocomial pathogen, especially in ICUs, transplant units, and oncology wards.
- Resistance is acquired, primarily via vanA or vanB genes on transposons or plasmids.
- VanA confers high-level resistance to vancomycin and teicoplanin, while vanB gives variable vancomycin resistance but teicoplanin susceptibility.
- Colonization (especially in the gut) can precede infection and facilitate nosocomial spread.
- Hand hygiene and contact precautions are critical for preventing VRE outbreaks.
- Routine screening of high-risk patients (e.g., rectal swab on chromogenic agar or PCR) is recommended in outbreak settings.
- Linezolid, daptomycin, or tigecycline are therapeutic alternatives in VRE infections.
- VRE is resistant to many antibiotics besides vancomycin (e.g., aminoglycosides, β-lactams).
- E. faecalis is less frequently VRE; E. faecium is more likely to be multidrug-resistant.
- Always confirm high MICs (>32 µg/mL) with molecular methods in critical infections.
Further Readings
- https://pubmed.ncbi.nlm.nih.gov/31329096/
- https://www.sciencedirect.com/science/article/pii/S0196655312001824
- https://www.sciencedirect.com/science/article/pii/S0196655312001824
- https://www.nature.com/articles/s41564-025-01958-0
- https://www.cdc.gov/vre/about/index.html
- https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2013.00048/full
- https://www.health.wa.gov.au/~/media/Corp/Documents/Health-for/Infectious-disease/HISWA/VRE-OD-2014.pdf
- https://link.springer.com/article/10.1007/s10096-011-1412-x