Metronidazole Resistance and Prevalence of Virulence Factor Genes in Enterotoxigenic Bacteroides Fragilis (Etbf) Strains Isolated From Patients With Colorectal Polyps Publisher



Sabour S ; Asli M ; Alaei H ; Nasoohian N ; Biglari Nejad M ; Mohagheghzadeh N ; Soleiman Meigooni S ; Mohsenzadeh A ; Serati P ; Azimi T
Source: Gene Reports Published:2026

Abstract

Background: Considering the increasing importance of antibiotic resistance in anaerobic bacteria and their potential role in colorectal disease progression, the present study aimed to determine the prevalence of metronidazole resistance and investigate the frequency of genes encoding virulence factors in B. fragilis isolates from patients with colorectal polyps. Methods: A total of 68 B. fragilis strains were isolated from 68 patients with colorectal polyps. Liofilchem® MIC Test strips were used to assess the susceptibility of B. fragilis isolates to metronidazole. The presence of the nimH gene was determined using a PCR assay. The prevalence of genes encoding virulence factors (katB, sod, and ftn) was determined using the PCR assay. Results: Out of the total 68 confirmed isolates of B. fragilis, 41 isolates, which constitute 60.3%, tested positive for the bft gene and are thus classified as ETBF. The results showed that 14.7% (n = 10/68) of B. fragilis isolates were resistant to metronidazole. In contrast, only 4.4% of B. fragilis isolates (n = 3/68) were positive for the nimH gene. 13.2% (n = 9/68), 47.1% (n = 32/68), and 44.1% (n = 30/68) of B. fragilis isolates were positive for katB, ftn, and sod genes, respectively. All (100%) metronidazole-resistant B. fragilis isolates were positive for the bft gene (P = 0.005). Out of 10 metronidazole-resistant B. fragilis isolates, 5 isolates were bft+/nimH-/katB−/ftn−/sod-. Conclusion: There was a statistically significant relationship between ETBF and resistance to metronidazole. Moreover, the presence of katB, sod, and ftn genes showed a significant relationship with COVID-19 history, non-smoking status, and obesity, respectively. © 2026 Elsevier Inc. All rights are reserved, including those for text and data mining, AI training, and similar technologies.