en fish disease fish disease پژوهشي Orginal research papers <p style="margin: 0in 0in 10pt; text-align: justify; unicode-bidi: embed; direction: ltr;"><span style="font-size:11pt"><span style="line-height:120%"><span sans-serif="" style="font-family:Calibri,"><span lang="TR" style="font-size:12.0pt"><span style="line-height:120%"><span new="" roman="" style="font-family:" times=""><span style="color:black">The extraction method and particularly the type of solvents used in the procedure are one of the most crucial steps for isolating antimicrobial compounds and extracts that potentially affect various microorganisms. This study aimed to evaluate the effects of water, ethanol (100%), methanol (100%), ethanol-water (50:50), and methanol-water (50:50) burdock (<i>Arctiumlappa</i>) root extracts (BE) on total phenol content and polyphenols as well as the antioxidant activity. In the next step, the solvent with the highest efficiency to have phenolic compounds were selected and employed to investigate the antibacterial effects of BE on the pathogenic bacterial strains (<i>i.e. Yersinia ruckeri</i>, <i>Lactococcus garvieae</i>, <i>Pseudomonas putida</i> and <i>Aeromonas hydrophila</i>) in rainbow trout (<i>Oncorhynchus mykiss</i>) by using disc diffusion test and tube dilution techniques. Maximum mean total phenolic content and antioxidant capacity were detected in the water-methanol mixture. Additionally, <em><span style="background:white">High-performance liquid chromatography</span></em><span style="background:white">(<em>HPLC</em>)</span> analysis revealed that both hesperidin and trans-ferulic acid compounds existed in all solvents. The antimicrobial activity of water-methanol BE was varied based on the type of microorganism. In this context, <i>Y</i>. <i>ruckeri</i> as a gram negative bacterium was found to be the most susceptible one compared to other pathogens. According to our findings, water-methanol solvent was more efficient to isolate phenolic compounds and exert antioxidant capacity, as the level of phenolic compounds in the extract was increased. Moreover, <i>Y. ruckeri</i> was recognized as the most sensitive pathogen in all tests. </span></span></span></span></span></span></span></p> Polar and nonpolar solvents, Arctium lappa root extract, Antibacterial, Rainbow trout, Phenol 493 510 http://jifro.ir/browse.php?a_code=A-10-82-23&slc_lang=en&sid=1 M. Moayyed pariaakbary1355@gmail.com 100319475328460048993 100319475328460048993 No Horticultural Sciences- Physiology and breeding medicinal plant, Department of Horticulture Faculty of Agriculture, Islamic Azad University Shiraz Branch, Shiraz,Iran. A.R. Eftekharian pariaakbary1355@gmail.com 100319475328460048994 100319475328460048994 No Horticultural Sciences- Physiology and breeding medicinal plant, Department of Horticulture Faculty of Agriculture, Islamic Azad University Shiraz Branch, Shiraz,Iran. M.S. Fereiduni saeid.fereidouni@gmail.com 100319475328460048995 100319475328460048995 No Aquatic Animal Health Unit, School of Veterinary Medicine, Shirazu University, Shiraz, Iran P. Akbary paria.akbary@gmail.com 100319475328460048996 100319475328460048996 Yes Fisheries Group, Marine Sciences Faculty, Chabahar Maritime University, Chabahar, Iran