A Shigella sp. variant is causally linked to intractable functional constipation

Functional constipation (FC) with intractable nature is the most severe form of constipation, but its etiology has long been unknown. In light of the intractable nature, we hypothesized that such intractable FC (IFC) sufferers were caused by intractable infection of a pathogenic bacterium. Here, we isolated a bacterium of Shigella sp. PIB from IFC patients that significantly inhibited the peristaltic contraction of colon by production of docosapentaenoic acid (DPA). PIB could colonize mice at least for six months. Oral administration of PIB was sufficient to induce constipation, which was reversed by PIB-specific phages. The mutated PIB with reduced DPA was incapable of inhibiting colonic function and inducing constipation, suggesting that DPA produced by PIB was the key mediator for the genesis of constipation. The PIB were detected in stools of 56% (38/68) of the IFC patients, but not in non-IFC or healthy populations (0/180). DPA levels in stools were elevated in 44.12% (30/68) of the IFC patients, but none of the healthy volunteers (0/97). Our results suggest Shigella sp. PIB may be the critical causative pathogen for IFC, and detections of fecal PIB bacteria plus DPA may be reliable methods for IFC diagnosis and classification.