en Food Safety and Hygiene Food Safety and Hygiene پژوهشي Original Article <div style="text-align: justify;"><span style="line-height:1;"><span style="font-size:14px;"><span style="font-family:Times New Roman;"><b><span lang="EN-GB">Background: </span></b><span lang="EN-GB">Rainbow trout (<i>Oncorhynchus mykiss</i>), an economically important fish in Iran, is valued for its nutritional potential. <i>Aeromonas hydrophila</i> causes infections that lead to motile septicaemia in fish and humans worldwide. Given the rapid expansion of fish farming in Iran, particularly in Zanjan Province, and the associated losses due to bacterial infections, this study aimed to detect <i>A. hydrophila</i> in farmed rainbow trout using molecular methods.</span><br> <b><span lang="EN-GB">Methods:</span></b><span lang="EN-GB"> A total of 103 fish samples were collected from ponds across five cities in Zanjan Province. Cultured specimens were subsequently analyzed, and <i>A. hydrophila</i> isolates were confirmed through standard biochemical tests. Genomic DNA was extracted from the isolates, and the <i>aerA</i> and <i>lip</i> genes were identified as markers for confirmation of <i>A. hydrophila</i> using the PCR method.</span><br> <b><span lang="EN-GB">Results:</span></b> <span lang="EN"><span style="color:#202124">Overall, 72 (69.90%) samples were positive for A. hydrophila, as determined by both culture and biochemical tests. However, molecular analysis confirmed the aerA gene in 66 (64.07%) of the isolates, while only 3 (2.91%) samples carried both the lip and aerA genes.</span></span><span lang="EN-GB"><span style="font-family:Gulliver"></span></span><br> <b><span lang="EN-GB">Conclusion:</span></b><span lang="EN-GB"> The high prevalence of <i>A. hydrophila</i> in rainbow trout poses a threat to public health and results in significant economic losses in aquaculture. Collaboration among epidemiologists, microbiologists, veterinarians, and food safety experts is essential to reduce these impacts.</span></span></span></span></div> Aeromonas hydrophila, Rainbow trout, PCR, aerA gene, lip gene, 47 51 http://jhehp.zums.ac.ir/browse.php?a_code=A-10-695-1&slc_lang=en&sid=1 Shahrzad Daneshamooz daneshamooz.shahrzad@yahoo.com 100319475328460016560 0000000154741793 Yes Department of Microbiology, School of Medicine, Zanjan University of Medical Sciences, Zanjan, Iran. Habib Zeighami zeighami@zums.ac.ir 100319475328460016561 0000000174671147 No Department of Microbiology, School of Medicine, Zanjan University of Medical Sciences, Zanjan, Iran. Fakhri Haghi haghi@zums.ac.ir 100319475328460016562 0000000328808821 No Department of Microbiology, School of Medicine, Zanjan University of Medical Sciences, Zanjan, Iran.