Tehran University of Medical Sciences Iranian Journal of Public Health 2251-6085 51 12 2022 12 17 2783 2790 Sara Kazemi Rad 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 Mohamad Reza Razavi Department of Parasitology, Pasteur Institute of Iran, Tehran, Iran 2021 10 05 2022 01 16 Background: Listeria monocytogenes is a gram positive, facultative intracellular bacteria and it is a causative agent of listeriosis. Abortion is one the most important side effect of listeriosis. Nano chitosan is widely used as nanomaterials considered due to its characteristics such as bactericidal and nontoxicity activity. The aim of this study was isolation of L. monocytogenes bacteria from pregnant women vaginal samples and evaluation of chitosan nanoparticles effects against them. Methods: Overall, 100 vaginal specimens were collected from pregnant women with and without a history of abortion referred to Tehran's Hospitals from Sep 2019 to Jul 2020 with questionnaires. Then, using biochemical methods, L. monocytogenes bacteria were isolated and identified. Isolated L. monocytogenes strains were confirmed using PCR and evaluation of prfA gene, which is the main gene for identification of this bacterium. The effect of chitosan nanoparticles was evaluated in comparison with the antibiotics used based CSLI guideline on isolated bacteria by well diffusion method. MIC and MBC were determined for nanoparticle at the end. Results: Five strains of L. monocytogenes that were confirmed by PCR method. Moreover, a statistically significant relationship was observed between the isolated strains and the samples taken from women with a history of abortion. MIC and MBC for L. monocytogenes ATCC 7644 were 156.25 and 312.5 μg/ml and for 5 isolated strains were 78.12 and 158.25 μg/ml, respectively. Conclusion: L. monocytogenes could be a causative agent of abortion in pregnant women. Concerning the results, Nano chitosan has acceptable antibacterial activity against L. monocytogenes.   https://ijph.tums.ac.ir/index.php/ijph/article/view/26492 https://ijph.tums.ac.ir/index.php/ijph/article/download/26492/7809