# Comparative analysis of vancomycin-resistant enterococci in colonization and infection—a longitudinal study

## TL;DR

This study compares VREfm isolates from colonization and infection to understand how they transition, finding no major genetic or phenotypic differences.

## Contribution

The study provides new insights into the lack of bacterial differences between colonization and infection, emphasizing host-pathogen interactions.

## Key findings

- No significant differences were found in genotypic or phenotypic traits between colonization and infection isolates.
- Colonization isolates were genetically closely related to infection isolates in 81% of cases.
- Host-pathogen interactions are suggested to play a key role in the transition from colonization to infection.

## Abstract

Vancomycin-resistant Enterococcus faecium (VREfm) carriage in the gastrointestinal tract is a risk factor for the development of an invasive infection. The exact mechanisms underlying the transition from colonization to infection are still unclear. We conducted a longitudinal study, including 54 paired VREfm isolates, consisting of a colonization and a subsequent bloodstream isolate from the same patient. We performed whole-genome sequencing, biofilm formation assays, and spot-on-lawn assays to investigate genotypic and phenotypic characteristics of the isolates. No significant differences in these characteristics between paired colonization and infection isolates were detected. Genotyping revealed that colonization isolates were genetically closely related to their respective infection isolates in 22 of 27 (81%) isolate pairs. Further studies focusing on the interaction between host epithelium and pathogen are needed to gain more insight into the transition from colonization to infection.

Previous studies have primarily focused on patient-related risk factors associated with the development of vancomycin-resistant Enterococcus faecium (VREfm) infection. However, identifying and characterizing the bacterial factors responsible for this transition is crucial, especially given the limited treatment options for VREfm infection. Our analyses revealed no significant differences between colonization and infection isolates, suggesting that host-pathogen interaction may play a more critical role in this progression and should be further investigated. Moreover, our findings highlight the importance of risk assessment and infection prevention measures to prevent VREfm colonization as a critical step in the development of VREfm infection.