Enterococcus faecium as an Emerging Pathogen: Molecular Epidemiology and Antimicrobial Resistance in Clinical Strains

Abstract

Vancomycin-resistant Enterococcus faecium represents an emerging threat in healthcare settings. The aim of this study was to investigate biomolecular characteristics of 31 E. faecium isolates from patients in two hospitals of Molise region, central Italy. Particularly, antimicrobial resistance profiles and prevalence of resistance and virulence genes were analyzed, as well as the clonal relationships and sequence types (STs). Antimicrobial susceptibility and genes associated with resistance and virulence were evaluated using automated system and PCR assays, respectively. SmaI-based pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing were performed following standardized protocols. All strains exhibited resistance to vancomycin and teicoplanin, and high rates were detected for other antibiotics, except for linezolid. PFGE identified 18 clusters and 26 pulsotypes (Simpson’s index, 0.98). ST80, ST1478, and ST2164 were identified, with ST80 as the most frequent (77.4%). The resistance genes vanA, aac(6′)-Ie-aph(2″)-Ia, aph(3′)-IIIa, and ermB were detected in 90.3%, 93.6%, 93.6%, and 90.3% of the strains, respectively, while the esp gene was prevalent (61.3%) amongst virulence genes. The study findings highlight the predominance of multidrug-resistant clones and virulence determinants among E. faecium strains circulating in the regional hospitals, reinforcing the urgency of implementing targeted molecular surveillance and robust antimicrobial stewardship strategies to contain their spread.