Faculty of Veterinary Medicine, Urmia University Veterinary Research Forum 2008-8140 Articles in Press 2026 08 02 The importance of plasmids in the development of antibiotic resistance in P. multocida 738356 10.30466/vrf.2025.2059477.4745 EN Mohammad Tabatabaei Department of Pathobiology, School of Veterinary Medicine, Shiraz University, Shiraz, Iran 0000-0002-3743-6583 Seyed Mehdi Joghataei Department of Microbiology and Immunology, Faculty of Veterinary Medicine, University of Tehran, Tehran, Iran 0000-0002-1572-9473 Journal Article 2025 05 01 An emerging global threat is the development of resistance to various antibiotic groups among pathogenic bacteria, including P. multocida, The excessive use of antibiotics and presence of antibiotic resistance carriers play a significant role in the development of multiple resistances to antimicrobial agents. Given the role and importance of plasmids in the development of antibiotic resistance, it is important to prevent the transfer, replication, and multiplication of plasmids by eliminating plasmids. In this study, the role of plasmids in the development and transmission of antibiotic resistance in P. multocida was investigated and evaluated. This study was performed on of P. multocida isolates were collected from apparently healthy and ailing animals (February to September 2014). Identification of P. multocida isolates using standard biochemical tests and kmt1 gene amplification. After initial tests and plasmid DNA extraction, five plasmid-containing isolates were selected for further work. To compare antibiotic resistance after plasmid removal, the disk diffusion method was used. Based on the results, it was determined that all plasmid-containing isolates that showed a high level of antibiotic resistance (especially with large plasmids) became sensitive to antimicrobial agents after plasmid removal. Therefore, according to the results obtained, the role and importance of plasmids in the development of antibiotic resistance in P. multocida is determined. It was also determined in this study that the existence and persistence of plasmids by P. multocida bacteria is of great importance in the role of plasmids in the development of antibiotic resistance.