Tehran University of Medical Sciences Iranian Journal of Microbiology 2008-3289 15 4 2023 08 27 533 540 EN Fardin Sheydai Department of Microbiology, Faculty of Veterinary Medicine, Urmia University, Urmia, Iran Amir Tukmechi Department of Microbiology, Faculty of Veterinary Medicine, Urmia University, Urmia, Iran 2023 04 05 2023 08 06 Background and Objectives: Instead of antibiotics, propolis is a promising alternative for treating bacterial diseases. The aim of this study was to evaluate the effect of propolis ethanol extract (PEE) on Yersinia ruckeri (Y. ruckeri), a fish pathogen, by examining its impact on the cell wall, cytoplasmic membrane, and gene expression. Materials and Methods: The effect of propolis on the bacterial cell wall, membrane, and DNA using scanning electron microscopy (SEM) was investigated. Its effect on the NAD+/NADH ratio, reactive oxygen species (ROS) production, as well as the expression of a virulence factor (yrp1) was also determined. Results: It was demonstrated that PEE has multiple antibacterial mechanisms against Y. ruckeri involving cell wall damage, membrane lysis, and a decrease in gene expression. Conclusion: The obtained results indicated that the mode of propolis action against Y. ruckeri is both structural and functional, while others showed propolis only could inactivate bacteria in a structural way. https://ijm.tums.ac.ir/index.php/ijm/article/view/4179 https://ijm.tums.ac.ir/index.php/ijm/article/download/4179/1597