Fusobacterium nucleatum Causes Microbial Dysbiosis and Exacerbates Visceral Hypersensitivity in a Colonization-Independent Manner

Abstract

<b>Background:</b> Microbial dysbiosis is closely associated with visceral hypersensitivity and is involved in the pathogenesis of irritable bowel syndrome (IBS), but the specific strains that play a key role have yet to be identified. Previous bioinformatic studies have demonstrated that <i>Fusobacterium</i> is a shared microbial feature between IBS patients and maternal separation (MS)-stressed rats. In this study, we assessed the potential role of <i>Fusobacterium nucleatum</i> (<i>F. nucleatum</i>) in the pathogenesis of IBS. <b>Methods:</b> Fecal samples of patients with diarrhea predominant-IBS (IBS-D) and healthy controls were obtained. An MS rat model was established to receive gavage of either <i>F. nucleatum</i> or normal saline. Visceral sensitivity was evaluated through colorectal distension test, and fecal microbiota was analyzed by 16S rRNA gene sequencing. <i>F. nucleatum</i>-specific IgA levels in fecal supernatants were assessed by western blotting. The antigen reacted with the specific IgA of <i>F. nucleatum</i> was identified by mass spectrometry and the construction of a recombinant <i>Escherichia coli</i> BL21 (DE3). <b>Results:</b> IBS-D patients showed a lower Shannon index and a higher abundance of <i>Fusobacterium</i>. The <i>F. nucleatum</i>-gavage was shown to exacerbate visceral hypersensitivity in MS rats, with both the <i>F. nucleatum</i>-gavage and MS causing a decreased Shannon index and a clear segregation of fecal microbiota. In addition, specific IgA against <i>F. nucleatum</i> was detected in fecal supernatants of both the <i>F. nucleatum</i>-gavaged rats and the IBS-D patients. The FomA protein, which is a major outer membrane protein of <i>F. nucleatum</i>, was confirmed to react with the specific IgA of <i>F. nucleatum</i> in fecal supernatants. <b>Conclusion:</b> <i>Fusobacterium</i> increased significantly in IBS-D patients, and <i>F. nucleatum</i> was involved in the pathogenesis of IBS by causing microbial dysbiosis and exacerbating visceral hypersensitivity in a colonization-independent manner. Meanwhile, <i>F. nucleatum</i> was found to induce an increase in specific secretory IgA through FomA.