Tracking persistent and resistant Enterococcus faecalis and E. faecium from farm to fork: biofilm-linked risks in antibiotic resistance of isolates

This study aimed to investigate the prevalence, antimicrobial resistance, biofilm-forming ability, virulence gene profiles, and associated risk levels of Enterococcus faecalis and E. faecium isolated along the farm-to-fork meat production continuum in Kayseri, Türkiye. Out of 348 samples analyzed, Enterococcus spp. were detected in 209 (60%) of the samples, of which 41 (20%) were E. faecalis and 48 (23%) were E. faecium. Both strains were resistant to at least one antimicrobial agent, and 35 isolates (39%) exhibited multidrug resistance (MDR). Among the tested antibiotics, resistance rates were particularly high for tetracycline (66% in E. faecalis, 69% in E. faecium) and erythromycin (56% and 58%, respectively); resistance to vancomycin (10% in each species) and ciprofloxacin (12% in E. faecalis and 13% in E. faecium) was low but consistently occurred in combination with resistance to other antibiotics and exclusively within multidrug resistance patterns. All isolates formed biofilms, with 55% being strong producers, of which 88% carried the gelE and/or efa gene. Strong biofilm formation was correlated with higher MDR rates (51% in strong biofilm producers and 25% in weak producers), peaking at 58% in E. faecalis strong producers. Risk scoring classified up to 40% of isolates as high risk. These findings suggest that enterococci may contribute to food contamination and serve as potential reservoirs of resistance and virulence, underscoring the relevance of farm-level hygiene, rational antibiotic use, and targeted surveillance within a One Health framework.