Tracking the Prevalence of Antibiotic Resistance in Enterococcus Within the Spanish Poultry Industry: Insights from a One Health Approach

<b>Background</b>/<b>Objectives</b>: Antimicrobial resistance (AMR) in <i>Enterococcus</i> species from poultry production represents a significant public health threat due to the potential transmission of AMR through the food chain. This study aimed to examine the relative prevalence, resistance patterns, and mannitol fermentation capacity of <i>Enterococcus</i> isolates from various poultry production systems in Spain over a seven-year period (2017-2023). <b>Methods</b>: A total of 215 <i>Enterococcus</i> isolates were analyzed. Phenotypic assessments were conducted to determine resistance rates and metabolic capacities, while genotypic characterization focused on detecting vancomycin-resistance genes (<i>vanA</i>, <i>vanB</i>, <i>vanC</i>, and <i>vanD</i>). <b>Results</b>: <i>Enterococcus faecalis</i> (62.3%) and <i>Enterococcus faecium</i> (29.77%) were the predominant species, primarily isolated from broilers (74.88%), with the highest frequency observed in one-week-old chicks (31.16%). High resistance rates to tetracyclines and streptogramins were identified, while resistance to vancomycin (0.47%) and tigecycline (3.03%) was low. Interestingly, a significant reduction in tetracyclines resistance was shown in this period for <i>Enterococcus faecalis</i> (from 100% to 70% (2017-2023) and <i>Enterococcus faecium</i> (from 100% to 40% (2018-2023)). Multidrug resistance (MDR) was detected in 26.98% of isolates. Mannitol fermentation tests revealed high metabolic capacity in <i>Enterococcus faecalis</i> (99.25%) and <i>Enterococcus faecium</i> (96.88%), associated with adaptability and virulence potential. Genotypic analysis showed a very low prevalence of <i>vanB</i> and <i>vanC</i> genes. <b>Conclusions</b>: These findings highlight the critical need for targeted surveillance and intervention strategies in poultry production to mitigate the risks posed by MDR <i>Enterococcus</i> to public health.