Tehran University of Medical Sciences Iranian Journal of Microbiology 2008-3289 17 5 2025 10 14 804 813 EN Manizheh Hajizadeh Varzeghan Department of Biology, Science and Research Branch, Islamic Azad University, Tehran, Iran Gholamreza Zarrini Department of Animal Biology, Faculty of Natural Sciences, University of Tabriz, Tabriz, Iran Farzam Sheikhzadeh Hesari Department of Animal Biology, Faculty of Natural Sciences, University of Tabriz, Tabriz, Iran Mohammad Hossein Modarressi Department of Medical Genetics, School of Medicine, Tehran University of Medicine Sciences, Tehran, Iran 2024 12 21 2025 07 17 Background and Objectives: Probiotics are effective in improving inflammatory bowel disease (IBD). This study assessed the effect of mesalazine and two candidate probiotics on the improvement of acetic acid (AA)-induced colitis model. Materials and Methods: Lactobacillus plantarum MS1and Lactobacillus delbrueckii YN1 were used for IBD model in rat. Twenty-five male Wistar rats weighing 250 ± 50 grams were used in 5 classified groups: Control (CO); Colitis (CL); Colitis, Probiotic (CLP); Colitis, Mesalazine (CLM); Colitis, Probiotic, Mesalazine (CLPM) and the treatment period was 3 weeks. The rats were treated with mesalazine 30 mg/kg and probiotic 109 CFU/ml after induction of colitis. Histopathological and immunological analyses were performed to evaluate the effects of probiotic bacteria on IBD. Results: The results showed that the probiotic bacteria reduced inflammation (P<0.05), extent (P<0.01), crypt abscesses (P<0.01), edema (P<0.05), inflammatory cell infiltration (P<0.5), and increased mucosa (P<0.001) in rats. Mesalazine administration in animals with colitis did not have a significant effect. Administration of probiotics in both CLP and CLPM groups reduced extent, crypt abscesses, edema, and inflammatory cell infiltration and showed an important role in the down-regulation of consolidation of pro-inflammatory factors (TNFα, IL-6, and IL-17), as well as up-regulation of anti-inflammatory factors such as IL-10. Conclusion: Lactobacillus plantarum MS1 and Lactobacillus delbrueckii YN1 have shown significant potential in alleviating AA-induced colitis symptoms. Their administration leads to a marked reduction in pro-inflammatory cytokines such as TNF-α, IL-17, and IL-6, while enhancing IL-10 levels, indicating their promise as therapeutic candidates for inflammatory bowel disease (IBD). https://ijm.tums.ac.ir/index.php/ijm/article/view/5210 https://ijm.tums.ac.ir/index.php/ijm/article/download/5210/1826