Genetic diversity, antimicrobial resistance, and biofilm-associated virulence in clinical Enterococcus faecalis isolates from Hamedan, Iran

Enterococcus faecalis is a leading cause of hospital-acquired infections, exhibiting high-level antimicrobial resistance, robust biofilm-forming capacity, and diverse virulence traits. This study aimed to investigate the distribution patterns, antibiotic resistance profiles, biofilm formation ability, virulence gene presence, and genetic diversity of clinical E. faecalis isolates in Hamedan, Iran. Sixty E. faecalis isolates were recovered from diverse clinical samples across three hospitals. Antimicrobial susceptibility was assessed by disk diffusion and MIC methods. Biofilm formation was quantified using the microtiter plate assay. The presence of the gelE gene and gelatinase activity was determined by PCR and phenotypic assays. Genetic relatedness was evaluated using ERIC-PCR. The majority of isolates (96.67%) exhibited biofilm-forming ability, with 78.3% producing moderate to strong biofilms. Multidrug resistance was detected in 80% of isolates, including 56.7% vancomycin-resistant and 70% high-level gentamicin-resistant strains, with a gelE prevalence of 56.6%. A significant association was found between biofilm strength and both MDR (p < 0.001) and gelE presence (p = 0.0027). Gelatinase activity was confirmed in 82% of gelE-positive isolates. ERIC-PCR revealed high genetic diversity, with 50 unique types and seven clusters sharing ≥ 80% similarity. While some genetically similar isolates shared phenotypic traits, variability in biofilm production and gelE carriage was observed even among closely related strains. The partial discordance between genotype and phenotype underscores the need for integrated molecular and phenotypic surveillance to inform infection control and antimicrobial stewardship strategies. Further studies using high-resolution genotyping are warranted to elucidate the mechanisms underlying strain dissemination and pathogenicity.