# Genomic epidemiology of vancomycin-resistant Enterococcus faecium in Eastern Denmark from 2020 to 2022, and identification of vanB Tn1549 insertion sites

## TL;DR

This study analyzed vancomycin-resistant Enterococcus faecium in Denmark from 2020 to 2022, identifying new genomic patterns and Tn1549 insertion sites.

## Contribution

The study reports ten new chromosomal Tn1549 insertion sites in vanB VREfm isolates from Denmark.

## Key findings

- Most vanB isolates had Tn1549 inserted in araA2 or sir2 genes.
- Eight new chromosomal insertion sites were identified.
- Three isolates had Tn1549 on plasmids.

## Abstract

We aimed to describe the genomic epidemiology of vancomycin-resistant Enterococcus faecium (VREfm) in Eastern Denmark from 2020 to 2022, identify and characterise the vanB Transposon 1549 (Tn1549) insertion sites among vanB VREfm clones and identify emerging VREfm clones.

We analysed all VREfm from our routine diagnostic sequencing during the study period. Using the Seqsphere + v.8.2.0 software (Ridom GmbH, Münster, Germany, (http://www.ridom.de/seqsphere), minimum spanning trees were created to visualise clusters. Tn1549 insertion sites were determined by in silico PCR. Nanopore sequencing was performed to assemble the regions surrounding Tn1549, which helped determine the insertion site locations.

We included 2,437 isolates in the study. A total of 463 isolates carried vanA, 1,963 isolates carried vanB, and 11 isolates carried both genes. Of all isolates carrying vanB, 254 isolates had the Tn1549 inserted in the araA2 gene, 1,604 in the sir2 gene, and 116 in neither the araA2 nor sir2 genes. We identified eight chromosomal insertion sites other than in the araA2 and sir2 genes. Three isolates carried the Tn1549 on plasmids. No emerging clones were found.

We have described the genomic epidemiology during the study period and identified ten chromosomal Tn1549 insertion sites.

The online version contains supplementary material available at 10.1007/s10096-025-05091-y.