Tehran University of Medical Sciences Iranian Journal of Microbiology 2008-3289 15 5 2023 10 12 631 641 Reza Khaltabadi Farahani Department of Molecular Biology, Pasteur Institute of Iran, Tehran, Iran; Department of Molecular, Central Veterinary Laboratory, Iranian Veterinary Organization, Tehran, Iran Mina Ebrahimi-Rad Department of Biochemistry, Pasteur Institute of Iran, Tehran, Iran Nader Shahrokhi Department of Molecular Biology, Pasteur Institute of Iran, Tehran, Iran Amir Hossien Khaltabadi Farahani Department of Animal Science, Faculty of Agriculture and Natural Resources, Arak University, Arak, Iran Seyed Ali Ghafouri Department of Clinical Sciences, Faculty of Veterinary Medicine, Ferdowsi University of Mashhad, Mashhad, Iran Maryam Rezaei Department of Molecular Biology, Pasteur Institute of Iran, Tehran, Iran Safoora Gharibzadeh Department of Epidemiology, Pasteur Institute of Iran, Tehran, Iran Arash Ghalyanchi Langeroudi Department of Microbiology and Immunology, School of the Veterinary Medicine, University Tehran, Tehran, Iran Parastoo Ehsani Department of Molecular Biology, Pasteur Institute of Iran, Tehran, Iran 2023 01 18 2023 10 12 Background and Objectives: Antibiotic resistance is an indicator of the passively acquired and circulating resistance genes. Salmonella Gallinarum significantly affects the poultry food industry. The present study is the first study of the S. Gallinarum biofilm in Iran, which is focused on the characterization of the S. Gallinarum serovars and their acquired antibiotic resistance genes circulating in poultry fields in central and northwestern Iran. Materials and Methods: Sixty isolates of S. Gallinarum serovar were collected from feces of live poultry. The bacteria were isolated using biochemical tests and confirmed by Multiplex PCR. Biofilm formation ability and the antibacterial resistance were evaluated using both phenotypic and genotypic methods. The data were analyzed using SPSS software. Results: According to Multiplex PCR for ratA, SteB, and rhs genes, all 60 S. Gallinarum serovars were Gallinarum biovars. In our study, the antibiotic resistance rate among isolated strains was as follows: Penicillin (100%), nitrofurantoin (80%), nalidixic acid (45%), cefoxitin (35%), neomycin sulfate (30%), chloramphenicol (20%), and ciprofloxacin (5%). All isolates were susceptible to imipenem, ertapenem, ceftriaxone, ceftazidime, and ceftazidime+clavulanic acid. All sixty isolates did not express the resistance genes IMP, VIM, NDM, DHA, blaOXA48, and qnrA. On the other hand, they expressed GES (85%), qnrB (75%), Fox M (70%), SHV (60%), CITM (20%), KPC (15%), FOX (10%), MOXM (5%), and qnrS (5%). All S. Gallinarum isolates formed biofilm and expressed sdiA gene. Conclusion: Considering that the presence of this bacteria is equal to the death penalty to the herd, the distribution of resistance genes could be a critical alarm for pathogen monitoring programs in the region. This study showed a positive correlation between biofilm formation and 50% of tested resistance genes. Also, it was found that the most common circulating S. gallinarum biovars are multidrug-resistant. https://ijm.tums.ac.ir/index.php/ijm/article/view/4091 https://ijm.tums.ac.ir/index.php/ijm/article/download/4091/1609