Characterization of vanA-harboring plasmids supports differentiation of outbreak-related and sporadic vancomycin-resistant Enterococcus faecium isolates in a tertiary care hospital.

BACKGROUND: The prevention of vancomycin-resistant Enterococcus faecium (VREfm) infections and transmissions poses a major challenge to hospitals. Vancomycin resistance can be plasmid encoded; however, as the analysis of plasmids is challenging, so far only a few reports have provided a detailed characterization of plasmids in nosocomial VREfm transmission. Here we describe a nosocomial VREfm outbreak caused by a vanA positive ST80 isolate. vanA plasmid sequence data was used to distinguish outbreak-associated isolates from sporadic VREfm cases and to investigate the spread of this plasmid within the local VREfm population. METHODS: 446 VREfm isolates were collected from routine surveillance between 01/2022 and 02/2024 and analyzed using long-read whole genome sequencing (lrWGS). Genetic relatedness of isolates was evaluated based on core genome multilocus sequence typing (cgMLST). Genetically similar vanA plasmids were identified using a Mash based approach. RESULTS: 30 genetically similar VREfm isolates were identified in patients' screening and environmental samples. Infection control evaluation confirmed transmission through shared hospital rooms. All outbreak-related VREfm isolates, including environmental samples, carried a highly similar vanA plasmid (Mash distance of < 0.001) with an identical replicon type. After enhanced infection control measures were established, no new transmissions were detected. Comparison with additional VREfm isolates from the respective department showed no evidence for further plasmid transmission. CONCLUSIONS: Our study illustrates how vanA plasmid analysis can support the evaluation of VREfm transmission in hospitals. The outbreak-associated vanA plasmids were genetically highly similar, but could be clearly distinguished from other vanA plasmids in the local hospital population. Taken together, detailed analysis of hospital-associated vanA plasmids can improve our understanding of VREfm transmission and epidemiology.