Tehran University of Medical Sciences Iranian Journal of Public Health 2251-6085 49 2 2020 02 01 369 376 Sogol ALEBOUYEH Department of Microbiology, Faculty of Basic Sciences, Lahijan Branch, Islamic Azad University, Lahijan, Iran Mehdi ASSMAR Department of Microbiology, Faculty of Basic Sciences, Lahijan Branch, Islamic Azad University, Lahijan, Iran Mirsasan MIRPOUR Department of Microbiology, Faculty of Basic Sciences, Lahijan Branch, Islamic Azad University, Lahijan, Iran 2020 01 29 Background: After cellulose, chitin is one of the most important polymers in crustaceans, insects, and fungi. Chitosan is one of the most important derivatives of chitin, which has important characteristics including degradability, non-toxicity, and biocompatibility antimicrobial and antioxidant properties. Methods: Chitosan was extracted from Penaeus semisulcatus shrimp using chemical methods and the degree of its austenitization was determined using a sub-red spectrophotometer and XRD. The nanoparticles were then synthesized using the ionic gelation method and analyzed through SEM. The antimicrobial effects of nanoparticles were also evaluated using antimicrobial tests on Listeria monocytogenes and Salmonella typhi. Results: Nanoparticles have antimicrobial activity and can inhibit bacterial growth at different concentrations. Conclusion: Chitosan nanoparticles have an inhibitory effect on Listeria monocytogenes, which is a gram-positive bacterium.   https://ijph.tums.ac.ir/index.php/ijph/article/view/19590 https://ijph.tums.ac.ir/index.php/ijph/article/download/19590/6675