"Keeping us on our toes": a review of what clinicians need to know about vancomycin-variable Enterococcus

Area of Science:

• Microbiology
• Infectious Diseases
• Genetics

Background:

• Enterococcus faecium exhibits rising vancomycin resistance, often linked to the vanA gene cluster.
• Vancomycin-variable enterococci (VVE) are genotypically vanA-positive but phenotypically susceptible, posing diagnostic challenges.
• VVE can transition to vancomycin resistance upon vancomycin exposure, often due to regulatory gene mutations.

Purpose of the Study:

• To review the mechanisms, microbiology, and epidemiology of vancomycin-variable enterococci (VVE).
• To highlight the challenges in identifying VVE and the potential for treatment failure.

Main Methods:

• Review of international reports and scientific literature on VVE.
• Analysis of genotypic and phenotypic screening methods for VVE detection.
• Summary of reported mechanisms underlying the vanA genotypic-phenotypic mismatch.

Main Results:

• VVE are increasingly prevalent globally, associated with outbreaks.
• Mechanisms for vancomycin-variable resistance primarily involve regulatory elements of the vanA gene cluster.
• Standard laboratory methods may fail to detect VVE, requiring combined genotypic and phenotypic screening.

Conclusions:

• VVE represent a significant clinical challenge due to difficulties in identification and potential for vancomycin treatment failure.
• Clinicians must maintain vigilance for VVE, considering their prevalence and resistance potential.
• Routine implementation of both genotypic and phenotypic screening is crucial for accurate VVE diagnosis.