Ready-to-eat meat foods as potential vectors for the transmission of antibiotic-resistant Enterococcus faecium

Enterococcus faecium, a member of the human gut microbiota and the second most abundant enterococcal species after E. faecalis, is an important agent of healthcare-associated infection. Its high capacity to acquire antimicrobial resistance genes (ARGs) makes infections difficult to treat. This study investigated ready-to-eat (RTE) meat products, typical of central Italy, as potential vectors of antibiotic-resistant enterococci, focusing on E. faecium. A total of 148 enterococcal strains, 36 of which were identified as E. faecium, were isolated. Among 22 distinct clones, eight were resistant to tetracycline (TET), two also to linezolid (LZD), and one showed a multidrug-resistance phenotype. Antibiotic susceptibility was determined by minimum inhibitory concentration testing, supported by whole-genome sequence analysis. Both LZD-resistant strains harbored LZD resistance genes (optrA or a combination of optrA and poxtA), while only one isolate demonstrated horizontal gene transfer via conjugation. The isolates were further characterized for virulence factors and biofilm formation capacity, both under basal conditions and following exposure to simulated upper gastrointestinal transit. All eight TET resistant strains presented genotypic virulence traits. Following exposure to simulated upper gastrointestinal transit, these isolates demonstrated high survival rates, maintaining both their antibiotic resistance phenotypes and biofilm-forming capacity. These findings highlight the potential role of the analyzed RTE meat products as vehicles for virulent and antibiotic-resistant E. faecium strains capable of surviving upper gastrointestinal exposure. The study underscores the need to implement enterococci surveillance in the food sector to improve monitoring of resistant E. faecium and to limit its possible dissemination and association in clinical risks.