# Enterococci and VRE

> Enterococci and VRE for NEET-PG Microbiology: identification, intrinsic resistance, vanA and vanB genes, treatment choices and infection control.

- Canonical URL: https://prepelephant.com/topics/neet-pg/microbiology/enterococci-and-vre
- Exam / course: NEET-PG · Subject: Microbiology
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-14
- Last updated: 2026-10-14
- Reference basis: Ananthanarayan and Paniker's Textbook of Microbiology; Mandell, Douglas and Bennett's Principles and Practice of Infectious Diseases; Cowan and Steel's Manual for the Identification of Medical Bacteria
- How to cite: "Enterococci and VRE", PrepElephant, https://prepelephant.com/topics/neet-pg/microbiology/enterococci-and-vre

## Direct answer

Enterococci are catalase-negative Gram-positive cocci that grow on bile-aesculin agar and in 6.5 per cent sodium chloride, and they cause hospital-acquired urinary, wound, bloodstream and endocardial infections. They are intrinsically resistant to cephalosporins and clindamycin. Vancomycin-resistant enterococci (VRE) carry vanA or vanB gene clusters, and the gene type decides whether teicoplanin remains usable.

## What you must remember

- **Identification:** catalase negative, PYR and leucine aminopeptidase positive, growing on bile-aesculin agar and in 6.5 per cent sodium chloride, with Lancefield group D antigen in most isolates.
- **Common species:** Enterococcus faecalis is the commoner urinary isolate and is usually ampicillin susceptible, whereas E. faecium is more often ampicillin and vancomycin resistant.
- **Intrinsic resistance:** cephalosporins, clindamycin and low-level aminoglycosides, so a cephalosporin result is expected rather than alarming.
- **High-level aminoglycoside resistance:** it abolishes the synergy of cell-wall agents with gentamicin, which changes the plan for endocarditis and other serious infection.
- **vanA:** high-level resistance to vancomycin and teicoplanin, inducible and carried on mobile elements.
- **vanB:** vancomycin resistance with teicoplanin usually preserved, so teicoplanin can remain an option for vanB strains.
- **Alternative drugs:** linezolid and daptomycin are used for VRE, and nitrofurantoin is reserved for uncomplicated urinary isolates.

## A stepwise route from isolate to therapy

A urine isolate from a catheterised patient in the medical ward raises questions about species, resistance pattern and infection control. Each step narrows the diagnosis and the drug choice.

1. **Confirm the genus:** catalase negativity, bile-aesculin growth and salt tolerance support the identification, and MALDI-TOF or a biochemical panel confirms the species.
2. **Read the intrinsic pattern:** cephalosporin resistance is expected in any enterococcus, so the team does not treat it as an unusual finding.
3. **Test ampicillin and vancomycin:** ampicillin resistance is common in E. faecium, and a raised vancomycin MIC triggers a check for VRE.
4. **Identify the vancomycin gene:** PCR for vanA and vanB separates high-level resistance from vanB resistance, which decides whether teicoplanin can be used.
5. **Match the site to the drug:** uncomplicated cystitis is treated with nitrofurantoin, while endocarditis calls for ampicillin with ceftriaxone for E. faecalis, per current guidance.
6. **Apply infection control:** contact precautions, dedicated equipment and hand hygiene are used, since VRE colonises the gut and survives on hospital surfaces.

## Where the exam tries to catch you

Enterococci look like streptococci on the bench, and the resistance questions turn on a few precise facts.

- **Trap:** choosing a cephalosporin for an enterococcal infection because it is broad spectrum — **Correct:** enterococci are intrinsically cephalosporin resistant, so the choice fails whatever the dose.
- **Trap:** assuming teicoplanin always works against VRE — **Correct:** vanA strains resist teicoplanin as well, so the gene type matters before the drug is chosen.
- **Trap:** reading PYR positivity as proof of group A streptococcus — **Correct:** enterococci are also PYR positive, so catalase testing must come first.

## Frequently asked questions

### Which tests identify enterococci in the laboratory?
Enterococci are identified by catalase negativity, growth on bile-aesculin agar and in 6.5 per cent sodium chloride, and positive PYR and leucine aminopeptidase reactions. Automated systems or MALDI-TOF mass spectrometry then confirm the species.

### Why are enterococci resistant to cephalosporins?
Enterococci are resistant to cephalosporins because their penicillin-binding proteins have low affinity for these drugs. This intrinsic resistance is present whatever the dose, so cephalosporins should not be selected for enterococcal infection.

### What is the difference between vanA and vanB in enterococci?
VanA gives high-level resistance to both vancomycin and teicoplanin, while vanB gives vancomycin resistance with teicoplanin usually remaining active. Both gene types alter the peptidoglycan target to D-alanine-D-lactate, which reduces glycopeptide binding.

### Which drugs are used against vancomycin-resistant enterococci?
Linezolid and daptomycin are the main drugs used against vancomycin-resistant enterococci, and the choice depends on the site of infection and susceptibility results. Nitrofurantoin is reserved for uncomplicated urinary tract infection, where it reaches adequate urinary concentrations.