# Odoribacter splanchnicus inhibits toxin production in Clostridioides difficile: insights from clinical correlation and in vitro validation

## TL;DR

A gut bacterium called Odoribacter splanchnicus may help prevent harmful toxin production by Clostridioides difficile, a major cause of hospital-acquired diarrhea.

## Contribution

Odoribacter splanchnicus is identified as a novel protective commensal that inhibits C. difficile toxin production both clinically and in vitro.

## Key findings

- Higher levels of Odoribacter splanchnicus correlate with lower CDI severity in clinical samples.
- In vitro, O. splanchnicus reduces C. difficile toxin production without affecting bacterial growth.
- Toxin suppression is linked to reduced tcdB gene expression and increased sporulation.

## Abstract

Clostridioides difficile infection (CDI) is a leading cause of healthcare-associated diarrhea. Although gut microbiota dysbiosis is central to CDI, the specific commensal species that confer protection are not well defined.

We performed 16S rRNA sequencing on fecal samples from a clinical cohort of 30 CDI patients, 30 non-CDI diarrhea patients, 27 asymptomatic C. difficile carriers, and 30 healthy controls. To functionally validate the clinical finding, an in vitro anaerobic co-culture system was established between the Odoribacter splanchnicus type strain and C. difficile. Toxin protein levels in the supernatant were quantified by ELISA at multiple time points (24, 48, and 72 h). Sporulation was assessed via ethanol resistance assays, and the expression of toxin genes (tcdA/tcdB) was measured by quantitative PCR (qPCR).

Clinical analysis revealed a significant negative correlation between the abundance of Odoribacter splanchnicus and CDI severity. In vitro, a high initial ratio of O. splanchnicus significantly suppressed C. difficile toxin production during the stationary phase, without inhibiting bacterial growth. This reduction in vitro levels was accompanied by a concurrent increase in sporulation and was preceded by a downregulation of tcdB gene expression.

This work positions O. splanchnicus as a highly promising candidate for the development of next-generation, defined microbial therapeutics and provides a mechanistic foundation for future anti-virulence approaches to combat CDI.