Tehran University of Medical Sciences Iranian Journal of Microbiology 2008-3289 18 1 2026 02 14 55 66 EN Farzaneh Korani Department of Microbiology, Faculty of Medicine, Ilam University of Medical Sciences, Ilam, Iran; Clinical Microbiology Research Center, Ilam University of Medical Sciences, Ilam, Iran Nayeb Ali Rezvani Department of Clinical Biochemistry, Kermanshah University of Medical Sciences, Kermanshah, Iran Noorkhoda Sadeghifard Department of Microbiology, Faculty of Medicine, Ilam University of Medical Sciences, Ilam, Iran; Clinical Microbiology Research Center, Ilam University of Medical Sciences, Ilam, Iran Behrooz Sadeghi Kalani Department of Microbiology, Faculty of Medicine, Ilam University of Medical Sciences, Ilam, Iran; Clinical Microbiology Research Center, Ilam University of Medical Sciences, Ilam, Iran Reza Pakzad Department of Epidemiology, Faculty of Health, Ilam University of Medical Sciences, Ilam, Iran Parisa Asadollahi Department of Microbiology, Faculty of Medicine, Ilam University of Medical Sciences, Ilam, Iran; Clinical Microbiology Research Center, Ilam University of Medical Sciences, Ilam, Iran 2025 08 29 2025 12 07 Background and Objectives: Colorectal cancer (CRC) is a leading malignancy with multifactorial etiology, including genetic, environmental, and microbial factors. Bacteria such as Helicobacter pylori, pks⁺ bacteria, Enterococcus faecalis, and Bifidobacterium bifidum have been linked to CRC, though their roles remain controversial. Some may promote inflammation and genotoxicity, while others may confer protective effects. This study assessed the presence and relative abundance of these bacteria in colorectal FFPE tissue samples. Materials and Methods: This case-control study included three groups of FFPE tissue samples: tumor tissues from CRC patients (Tumor, n=50), normal tissues adjacent to tumors (Adjacent, n=50), and normal tissues from non-CRC individuals (Normal, n=30). Sections were prepared with a microtome, and bacterial gene copy numbers were quantified using species-specific primers and quantitative real-time PCR, normalized to human GAPDH. Associations with age, sex, and neoplastic type were analyzed (p < 0.05). Results: B. bifidum was significantly higher in Adjacent tissues compared to Tumor and Normal (p < 0.0001). H. pylori detection increased progressively from Normal to Adjacent to Tumor tissues (p = 0.002). pks⁺ bacteria were detected only in individuals ≥60 years (p = 0.014). E. faecalis load was higher in Tumor tissues of females and older adults, though overall presence did not differ significantly among groups. Conclusion: Enrichment of B. bifidum and increased H. pylori detection near tumors suggest the tumor microenvironment favors bacterial persistence. Age- and sex-related patterns in pks⁺ and E. faecalis highlight host influences on microbial distribution in CRC, supporting further mechanistic studies. https://ijm.tums.ac.ir/index.php/ijm/article/view/5746 https://ijm.tums.ac.ir/index.php/ijm/article/download/5746/1862