Tehran University of Medical Sciences Iranian Journal of Microbiology 2008-3289 14 5 2022 10 22 689 697 Farzaneh Nazari Department of Microbiology, Faculty of Sciences, Islamic Azad University, Arak Branch, Arak, Iran Parvaneh Jafari Department of Microbiology, Faculty of Sciences, Islamic Azad University, Arak Branch, Arak, Iran Bizhan Nomanpour Department of Microbiology, School of Medicine, Kermanshah University of Medical Sciences, Kermanshah, Iran Kambiz Varmira Department of Medicine, Research Center of Oils and Fats, Health Technology Institute, Kermanshah University of Medical Sciences, Kermanshah, Iran Farshid Raissi Department of Pathology, School of Medicine, Kermanshah University of Medical Sciences, Kermanshah, Iran 2022 02 25 2022 04 24 Background and Objectives: Breast cancer is the second leading cause of death and one of the most common malignancies among women in the world. The aim of this study was to investigate the preventive effects of postbiotic consisting of sonicated Bifidobacterium bifidum cells on triple negative breast cancer. Materials and Methods: Thirty-six female BALB/c mice aged 5-7 weeks were randomly divided into 3 groups (n=12): Ctrl-, healthy mice; Ctrl+, mice with breast cancer with no treatment; and Postbiotic, mice with orally gavage postbiotic before and after 4T1 cell line transplantation. Cancer progress and the effects of postbiotic were assayed by histological, immunohistochemical and gene expression quantification. Results: The histological results showed that administration postbiotic consisting of B. bifidum significantly decreased carcinogenesis in terms of tumor incidence, multiplicity and volume. The tumor progress was suppressed by oral intake of B. bifidum as showed by p53 and Ki-67 expression. Furthermore, Oral intake of postbiotic resulted in extended survival of mice and inhibited sever weigh loss. Conclusion: Pretreatment with sonication killed B. bifidum, as a postbiotic, inhibited breast cancer progress and malignancy. https://ijm.tums.ac.ir/index.php/ijm/article/view/3574 https://ijm.tums.ac.ir/index.php/ijm/article/download/3574/1507