# “Hiding in Plain Sight”: A Retrospective Clinical and Microbiological Review of Vancomycin-Dependent Enterococci at a Tertiary Care Centre—A Case Report

## TL;DR

This paper reports a rare case of vancomycin-dependent Enterococci in a liver transplant patient and emphasizes the need for improved clinical awareness and diagnostic methods.

## Contribution

The paper presents the first reported Canadian case of vancomycin-dependent Enterococci and highlights diagnostic and clinical challenges.

## Key findings

- Vancomycin-dependent Enterococcus faecium was identified in a liver transplant recipient.
- Four VDE cases were identified over two years, all from high-risk patients with prolonged glycopeptide exposure.
- Diagnostic challenges include failure to grow on standard media and the need for vancomycin-supplemented agar.

## Abstract

Vancomycin-resistant Enterococci (VRE) are established nosocomial pathogens; however, vancomycin-dependent Enterococci (VDE) represent a rare and underrecognized phenomenon. These organisms paradoxically require vancomycin for growth due to mutations in cell wall precursor synthesis. Limited awareness and significant diagnostic challenges associated with VDE can lead to delayed recognition and treatment failure. We report a case of vancomycin-dependent Enterococcus faecium isolated from a liver transplant recipient receiving oral vancomycin prophylaxis for recurrent Clostridioides difficile infection. The isolate failed to grow on standard media but exhibited robust growth on vancomycin-supplemented agar, confirmed by vancomycin disc diffusion testing and PCR detection of the vanB gene. Additionally, we reviewed four further VDE cases identified over a two-year period in our tertiary care microbiology laboratory. All patients originated from complex care settings, had significant comorbidities, and had received prolonged glycopeptide therapy. We summarize the clinical features, diagnostic findings, and microbiological challenges encountered across this case series. This series documents the first reported Canadian case of VDE and highlights the critical need for clinical vigilance and diagnostic suspicion in high-risk patients with prior enterococcal colonization and ongoing glycopeptide exposure. Laboratory findings such as failure to grow on blood agar coupled with growth around vancomycin discs should prompt specific evaluation for VDE. Our findings reinforce the necessity for targeted antimicrobial stewardship and infection prevention strategies and underscore the remarkable evolutionary adaptability of Enterococci under sustained antimicrobial pressure.