Faculty of Veterinary Medicine, Urmia University Veterinary Research Forum 2008-8140 Articles in Press 2026 06 25 The effects of agr -genotype on biofilm forming ability in Staphylococcus pseudintermedius isolates from broiler chickens 737020 10.30466/vrf.2025.2053976.4671 EN Sahar Nouri Gharajelar Department of Pathobiology, Faculty of Veterinary Medicine, Tabriz University, Tabriz, Iran. Pariya Heasri Master Student of veterinary bacteriology, Faculty of Veterinary Medicine, University of Tabriz, Tabriz, Masoumeh Firouzamandi Department of Pathobiology, Faculty of Veterinary Medicine, University of Tabriz, P.O. Box: 5166614779, Tabriz, Iran. Roghaiyeh Akbari Master Student of veterinary bacteriology, Faculty of Veterinary Medicine, University of Tabriz, Tabriz, Journal Article 2025 02 20 The accessory gene regulator(agr) operon as a part of the quorum-sensing (QS) system, is responsible for the regulation of numerous virulence factors in Staphylococci. Furthermore, the ability of the opportunistic pathogen, Staphylococcus pseudintermedius to form biofilm is a significant contributor to chronic diseases. Our aim was evaluation of the association between different agr groups and the expression of icaD gene related to biofilm formation among S. pseudintermedius from nasal samples. Fifty nasal swabs were collected from broiler chickens; then phenotypic and molecular tests performed for isolation of S. pseudintermedius from samples and their agr genotype was also investigated. The biofilm production capacity of the isolates was determined using both microtiter plate assay and amplification of icaD gene. S. pseudintermedius was detected in 86.84% of samples. The assessment of agr typing results related that most of the strains (69.70%) were classified in agr group ɪ. The relative frequency of biofilm producing S. pseudintermedius isolates was 75.76% and all of them harbored icaD gene. The expression level of icaD determinant was significantly higher among isolates in agr group ɪ than other agr groups. The results suggest that broiler chickens may act as a reservoir for transmission of S. pseudintermedius to humans which should be considered a potential zoonotic bacterium able to produce different virulence factors like biofilm.