Competition between vancomycin-resistant enterococci of different sequence types

Introduction

Vancomycin-resistant enterococci (VRE) are multi-drug-resistant organisms that cause severe nosocomial infections. VRE of sequence types (ST) ST80 and ST117 experience an upcoming prevalence in screening and clinical isolates in Germany. Since this national increase cannot be explained by transmission events, we hypothesize that VRE of these STs either have selective advantages or harbor an increased virulence potential resulting in enhanced numbers of infections. This study aims at identifying ST-specific phenotypic differences of VRE and to investigate whether ST117 and ST80 VRE dominate VRE of other ST in vitro.

Materials & Methods

VRE isolated from patients of a tertiary care hospital in 2021-2023 were subjected to whole genome sequencing and compared using a core genome Multilocus Sequencing Typing (cgMLST) approach. Biofilm production was investigated by crystal violet assay. Competition of VRE with different STs was analyzed in a Spot Killing Assay.

Results

Most frequently, VRE of ST117 and ST80 but also rarer ST2032, ST2481 and ST18 were identified. VRE of ST117 and ST80 showed a significant higher biofilm production compared to ST2481 and ST18 (ST2481: p = 0.006; p = 0.0002; ST18: p = 0.001, p = 2.9x10-7, respectively). Only one of two ST2032 produced biofilm. Spot Killing Assays resulted in inhibited growth of ST2481 and ST18 VRE after spotting ST117 and ST80 VRE or their respective supernatants.

Summary

In this study, we identified two explanations for the current trend of increasing VRE STs 117 and 80 in Germany. ST117 and ST80 VRE strains and their supernatants lyse VRE of other STs in vitro, indicating a possible intra-host selective advantage. Additionally, biofilm production of these predominant STs is enhanced compared to others, probably facilitating survival of these strains in the patient environment.