Relative abundance of a gut-derived Lancefieldella parvula strain is associated with severe inflammation in IBD

Lancefieldella parvula (previously known as Atopobium parvulum ) has been associated with inflammatory bowel disease (IBD); however, prior in vivo studies relied on an oral-derived reference strain rather than intestinal clinical isolates, limiting interpretation of its role in gut inflammation. To address this gap, we isolated a clinical strain of L. parvula (designated L. parvula TI19E08) from a mucosal luminal aspirate of an ulcerative colitis (UC) participant. We developed a strain-specific quantitative PCR assay to quantify its abundance across anatomical sites in treatment-naïve pediatric IBD participant (UC and Crohn’s disease (CD)) and examined its relationship with site-specific endoscopic inflammation severity. We demonstrated that the relative abundance of L. parvula TI19E08 increased with increasing local inflammation severity. In UC, both strain-specific and total L. parvula levels were strongly correlated with inflammation severity, particularly in the proximal colon. In CD patients, strain-level associations were most pronounced in the terminal ileum, which is consistent with the disease distribution. This study characterizes an intestinal L. parvula isolate and demonstrates that strain-level expansion correlates with disease severity across IBD subtypes and anatomical regions. These findings identify L. parvula TI19E08 as a candidate mucosal marker of inflammation severity in IBD patients.