VRE
One-Sentence Definition
VRE (vancomycin-resistant enterococci) are Enterococcus isolates — most often E. faecium — with acquired van gene clusters that remodel peptidoglycan termini so vancomycin (and often teicoplanin) can no longer bind.
Simple Explanation
The enterococcus changes the “hook” on its cell wall that vancomycin grabs, so the drug slips off — usually after picking up a mobile resistance cassette.
Detailed Scientific Explanation
| Genotype | Ligand change | Typical vancomycin | Teicoplanin |
|---|---|---|---|
| VanA | D-Ala-D-Lac | High-level R | R |
| VanB | D-Ala-D-Lac | Variable R | often S |
| VanC | Intrinsic (E. gallinarum/casseliflavus) | Low-level | S |
| VanD/E/G… | Less common | Variable | Variable |
- vanA often on Tn1546-like elements / plasmids (Transposons and Insertion Sequences, Plasmid)
- Inducible via Two-Component Regulatory Systems (VanRS) — exposure raises expression
- Host: predominantly Enterococcus faecium hospital clade; E. faecalis VRE less common but important
Mechanism
Van enzymes synthesize D-Ala-D-Lac (or D-Ser) ending precursors → vancomycin cannot bind depsipeptide with high affinity → cell wall synthesis continues.
Clinical Importance
- ICU/transplant bacteremia, device infection, endocarditis treatment crises
- Contact precautions; rectal screening in outbreaks (Infection Prevention and Control)
- Therapy: linezolid, daptomycin (optimize), sometimes tigecycline/combination — stewardship mandatory (Antimicrobial Stewardship)
- Risk of vanA transfer toward S. aureus (VRSA — rare but watched)
Research Importance
- Plasmid epidemiology of VRE; One Health links limited vs Gram-negatives but exist
- WGS/cgMLST for hospital clusters (Population Structure and Clustering)
Diagnostic Relevance
- Vancomycin MIC + confirm species (avoid calling intrinsic VanC organisms “VRE” in the same IPC sense)
- vanA/vanB PCR on isolates or screening swabs
- Antimicrobial Susceptibility Testing remains definitive for therapy
AMR Relevance
Flagship Gram-positive nosocomial AMR alongside MRSA; core ESKAPE Pathogens member.
Related Organisms
Related Methods
Related MOCs
Learning Aids
Clinical Example
Example
Case: Bone marrow transplant patient; blood culture E. faecium; vancomycin MIC >256; vanA PCR positive.
Question: Is teicoplanin likely active?
Answer: Usually no for VanA — choose an anti-VRE agent and source control; isolate for IPC.
Active Recall Questions
- VanA vs VanB — teicoplanin difference?
- Why can vancomycin MIC rise after drug exposure in inducible strains?
- Which organism most often carries hospital VRE?