Tehran University of Medical Sciences Iranian Journal of Microbiology 2008-3289 10 1 2018 02 26 51 58 EN Somayyeh Hosseinzadeh Department of Microbiology, Faculty of Veterinary Medicine, Urmia University, Urmia, Iran Habib Dastmalchi Saei Department of Microbiology, Faculty of Veterinary Medicine, Urmia University, Urmia, Iran Malahat Ahmadi Department of Microbiology, Faculty of Veterinary Medicine, Urmia University, Urmia, Iran Taghi Zahraei Salehi Department of Microbiology, Faculty of Veterinary Medicine, Tehran University, Tehran, Iran 2017 07 20 2018 02 10 Background and Objectives: Salmonellosis due to multi-drug resistant Salmonella Typhimurium with biofilm formation ability is a serious public health threat worldwide. Studies have shown that medicinal plants inhibit the growth of bacterial species. The present study aimed at determining antibiotic resistance pattern and biofilm formation ability of S. Typhimurium isolated from poultry flocks. Moreover, the antibacterial activity of Licochalcone A (LAA) and Epigallocatechin-3-gallate (EGCG) against the studied isolates were investigated in this study. Materials and Methods: Antibiotic susceptibility testing of S. Typhimurium RITCC1730 and 23 clinical isolates of S. Typhimurium against 8 antibiotics was performed using standard Kirby-Bauer disc diffusion method. The extent of biofilm formation was measured by Microtiter dish biofilm formation assay. Antimicrobials activities of LAA and EGCG were determined by MIC and MBC assays using microdilution method. Results: The highest antimicrobial resistance was detected against chloramphenicol (52.17%), followed by furazolidone (26.08%), and trimethoprim/sulfamethoxazole (21.73%). All isolates were sensitive to ciprofloxacin (100%), followed by gentamicin, imipenem (95.65%), and cefixime (91.30%). Most of the isolates (78.26%) were able to produce weak biofilm. LAA and EGCG inhibited the growth of S. Typhimurium at the MIC levels of 62.5~1000 and 1.56~400 µg/mL, respectively. The MBC value of LAA was >1000 µg/mL, while the corresponding value of EGCG varied from 100 to 800 µg/mL. Conclusion: S. Typhimurium isolates revealed a multiple antibiotic resistance with biofilm production ability. As a result, EGCG, and to a lesser extent, LAA displayed potential antibacterial activity against S. Typhimurium and could be considered as useful compounds for the development of antibacterial agents against salmonellosis.   https://ijm.tums.ac.ir/index.php/ijm/article/view/1435 https://ijm.tums.ac.ir/index.php/ijm/article/download/1435/781