Comparative genomics of hospital-associated vancomycin-resistant <i>Enterococcus faecium</i> from regional tertiary hospitals in Thailand

<h4>Background</h4>Vancomycin-resistant <i>Enterococcus faecium</i> (VREfm) poses a significant public health threat due to increasing antimicrobial resistance and virulence factors associated with severe infections. The primary objective was to investigate the genetic and phenotypic characteristics of 46 VREfm clinical isolates obtained from three tertiary hospitals in Thailand (2015-2019).<h4>Methods</h4>Phenotypic testing included antimicrobial susceptibility testing (AST) and virulence factor testing (gelatinase, lipase, protease, hemolytic activity, and biofilm formation), which were performed using standard laboratory methods. Short-read whole-genome sequencing (WGS) was performed to determine sequence types (ST), identify antimicrobial resistance and virulence genes, and perform phylogenetic analysis using SNP alignments.<h4>Results</h4>All isolates exhibited vancomycin and teicoplanin resistance, and γ-hemolysis was the predominant pattern (23 isolates). Biofilm formation was predominantly moderate to weak. Most isolates had multiple antimicrobial resistance and virulence-associated genes. Genotype and phenotype concordance were high for β-lactams, ciprofloxacin, and glycopeptides, whereas tetracycline (54.35%), streptomycin (45.65%), and gentamicin (45.65%) exhibited moderate concordance. Phylogenetic analysis revealed two major clades, Clade I (predominantly ST80) and Clade II (predominantly ST17). One isolate represented a novel ST, ST2331 (Clade I), which was identified from urine.<h4>Conclusion</h4>VREfm isolates from the three hospitals showed multidrug-resistant profiles and carried various resistance and virulence-associated genes. Whole-genome sequencing revealed two major phylogenetic clades. Overall, genotypic findings corresponded well with the phenotypic resistance patterns, with a small number of isolates showing genotype-phenotype discrepancies. These results highlight the genomic diversity and clinical relevance of VREfm circulating in Thai tertiary hospitals.