{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,11]],"date-time":"2026-08-11T16:14:39Z","timestamp":1786464879112,"version":"build-2736575974"},"reference-count":41,"publisher":"MDPI AG","issue":"8","license":[{"start":{"date-parts":[[2026,8,9]],"date-time":"2026-08-09T00:00:00Z","timestamp":1786233600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100003359","name":"Generalitat Valenciana","doi-asserted-by":"publisher","award":["CIAICO\/2021\/149"],"award-info":[{"award-number":["CIAICO\/2021\/149"]}],"id":[{"id":"10.13039\/501100003359","id-type":"DOI","asserted-by":"publisher"}]},{"award":["CIAICO\/2021\/149"],"award-info":[{"award-number":["CIAICO\/2021\/149"]}],"id":[{"id":"https:\/\/ror.org\/0097mvx21","id-type":"ROR","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Vet. Sci.","Veterinary Sciences"],"abstract":"<jats:p>Enterococcus faecalis and Enterococcus faecium are commensal bacteria of poultry but also important opportunistic pathogens and key indicators for antimicrobial resistance (AMR) surveillance within a One Health framework. However, data on the occurrence and antimicrobial resistance of enterococci in breeding hens remain limited despite their critical role in the poultry production pyramid. This study evaluated the prevalence, antimicrobial resistance profiles, and resistance genes of Enterococcus faecalis and Enterococcus faecium isolated from two commercial breeding hen farms in eastern Spain. A total of 330 isolates were obtained from different production stages and sample types. Species identification was performed by multiplex PCR, antimicrobial susceptibility was assessed using disk diffusion according to Clinical and Laboratory Standards Institute (CLSI) guidelines, and resistance genes (erm and tet) were detected by PCR. A significant age-related shift from E. faecalis in early production stages to E. faecium in adult hens was observed. High resistance rates were detected for tetracycline (up to 95.2%) and erythromycin, whereas resistance to critically important antimicrobials such as vancomycin, aminoglycosides, and ampicillin was rare or absent. Significant differences between farms were identified in both antimicrobial resistance levels and the prevalence of multidrug resistance. The most prevalent resistance genes were ermB, tetL, and tetM, frequently co-occurring. This study shows that breeding hens constitute a relevant reservoir of AMR within poultry production systems. Species dynamics and resistance patterns appear to be influenced by age and farm-related factors. These findings underscore the need for continuous AMR surveillance integrating phenotypic and genotypic approaches from a One Health perspective.<\/jats:p>","DOI":"10.3390\/vetsci13080795","type":"journal-article","created":{"date-parts":[[2026,8,10]],"date-time":"2026-08-10T10:23:50Z","timestamp":1786357430000},"page":"795","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Antimicrobial Resistance and Species Dynamics of Enterococcus faecalis and Enterococcus faecium in Breeding Hens: Phenotypic and Genotypic Characterization"],"prefix":"10.3390","volume":"13","author":[{"given":"Alejandro","family":"Fenollar","sequence":"first","affiliation":[{"name":"Biotechnology Department, Universitat Polit\u00e8cnica de Valencia. Cno. Vera s.n., 46022 Valencia, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-7961-9142","authenticated-orcid":false,"given":"Mar\u00eda A.","family":"Ferr\u00fas","sequence":"additional","affiliation":[{"name":"Centro Avanzado de Microbiolog\u00eda Aplicada, Universitat Polit\u00e8cnica de Valencia, Cno. Vera s.n., 46022 Valencia, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8298-102X","authenticated-orcid":false,"given":"Pablo","family":"Catal\u00e1-Gregori","sequence":"additional","affiliation":[{"name":"Centro de Calidad Av\u00edcola y Alimentaci\u00f3n Animal de la Comunidad Valenciana (CECAV), CEU Universities, Universidad CEU Cardenal Herrera, 46115 Alfara del Patriarca, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Vicente","family":"Tall\u00e1-Ferrer","sequence":"additional","affiliation":[{"name":"Grupo SADA, Ronda de Poniente 9, 28760 Tres Cantos, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6171-5171","authenticated-orcid":false,"given":"Miguel","family":"Garc\u00eda-Ferr\u00fas","sequence":"additional","affiliation":[{"name":"Centro Avanzado de Microbiolog\u00eda Aplicada, Universitat Polit\u00e8cnica de Valencia, Cno. Vera s.n., 46022 Valencia, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3329-7221","authenticated-orcid":false,"given":"Ana Isabel","family":"Jim\u00e9nez-Belenguer","sequence":"additional","affiliation":[{"name":"Centro Avanzado de Microbiolog\u00eda Aplicada, Universitat Polit\u00e8cnica de Valencia, Cno. Vera s.n., 46022 Valencia, Spain"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,8,9]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"European Food Safety Authority, and European Centre for Disease Prevention and Control (2025). The European Union summary report on antimicrobial resistance in zoonotic and indicator bacteria from humans, animals and food in 2022\u20132023. 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