Fusobacterium species are part of the gut microbiome in humans, but some species have been recognized as opportunistic pathogens implicated in inflammatory diseases including inflammatory bowel diseases. Here, we performed prevalence screening of Fusobacterium in ulcerative colitis (UC) in Japanese patients.

We examined Fusobacterium nucleatum (F. nucleatum) and whole Fusobacterium species (Pan-fusobacterium) by quantitative real-time PCR in 163 inflamed mucosae from 152 UC patients. Data were correlated with clinical subtypes of UC.

In an initial prevalence screen, F. nucleatum and Pan-fusobacterium were detected in 6.3 % (4/64) and 53.1 % (34/64). For all 163 mucosae, the prevalence of Pan-fusobacterium was 54.6 % (89/163). Pan-fusobacterium status was concordant in inflamed and normal adjacent samples, and the matched cases during 1-year follow-up colonoscopy. The higher amount of Pan-fusobacterium was observed in chronic continuous type compared to one attack and relapse/remitting type (p = 0.039). The higher amount of Pan-fusobacterium was also associated with rather mild clinical course of disease, such as non-steroid dependency (p = 0.015), non-refractory phenotype (p = 0.013), and non-severe phenotype (p = 0.04). Based on the distribution of Pan-fusobacterium measurable cases, we identified 10 cases as having a high amount of Pan-fusobacterium (FB-high). The clinicopathological features of FB-high UC cases were also highlighted by chronic continuous type and mild phenotypes of disease.

Whole Fusobacterium species, but not F. nucleatum, are common in UC patients and have a role in persistence of colonic inflammation in UC. However, Fusobacterium infection is associated with rather mild clinical phenotypes of UC.