Phenotypic and Genotypic Characterization of Enterococcus spp. from Poultry in Chile: Antimicrobial Resistance, Biofilm, and Virulence Genes

Enterococcus spp. are increasingly recognized as important opportunistic pathogens in poultry production and represent a potential One Health concern because of their virulence potential and capacity to acquire antimicrobial resistance determinants. This study characterized Enterococcus isolates recovered from clinical poultry cases in Chile, focusing on species distribution, virulence-associated genes, antimicrobial resistance patterns and genes, biofilm formation, and cytolysin activity. A total of 39 isolates were identified using the VITEK® 2 Compact system and confirmed by PCR targeting the tuf gene. Seven Enterococcus species were detected, with E. faecalis predominating (61.5%) and E. faecium following (15.4%). The virulence-associated genes asa1, gelE, and cylA were detected in 97.4%, 97.4%, and 48.7% of the isolates, respectively. Phenotypic antimicrobial susceptibility testing showed resistance mainly to tetracycline (61.5%) and erythromycin (17.9%), whereas all isolates were susceptible to vancomycin, ampicillin, chloramphenicol, and linezolid. Molecular analysis identified tetM (71.8%), ermB (66.7%), and tetL (30.8%) as the most predominant resistance genes. A significant association was observed between tetM and phenotypic tetracycline resistance (Fisher’s exact test, p = 0.010). However, no association was found between ermB and erythromycin resistance. Biofilm formation was observed in 66.7% of the isolates, although most were weak biofilm producers. Despite the relatively high prevalence of cylA, β-hemolytic activity was detected in only 5.1% of isolates, indicating an incomplete genotype–phenotype concordance. Overall, poultry-associated Enterococcus spp. circulating in Chile harbored multiple virulence and antimicrobial resistance determinants that may contribute to their persistence and adaptation in poultry production systems. These findings provide the first baseline molecular epidemiological data on clinical poultry-associated Enterococcus spp. isolates in Chile and support the need for continued surveillance and prudent antimicrobial use in veterinary medicine.