Evaluation of the efficacy of inactivated fecal transplants against Clostridioides difficile: an in vitro study

Fecal microbiota transplantation (FMT) requires rigorous donor screening, limiting donor eligibility and increasing costs. Recent evidence suggests that bacterial viability may not be essential for treating recurrent Clostridioides difficile infections. This study aimed to evaluate whether inactivated fecal preparations retain anti-C. difficile (CD) activity in vitro. Stool samples from three donors underwent eight different inactivation protocols, including mechanical, thermal, and chemical treatments. Bacterial viability and anti-CD activity were assessed by culture and inhibition assays. Mechanical filtration, pasteurisation, and sterilisation eliminated bacterial growth, while tyndallisation and ethanol treatments only partially reduced viability. Inhibition of CD growth was observed exclusively in samples containing live bacteria, with no significant difference compared to native stool. Inactivated samples, despite potentially retaining other microbiota-derived components, showed no anti-CD activity. These results suggest that live bacteria are essential for in vitro antagonism of C. difficile and thus in the therapeutic effects of FMT.