The role of biofilms in recurrent Clostridioides difficile infection and the interaction of C. difficile in multispecies biofilms

Clostridioides difficile infection (CDI) is the leading cause of infective antibiotic-associated diarrhoea and is responsible for significant patient morbidity and mortality. Despite appropriate antimicrobial therapy, CDI recurs in approximately 20-30 % of cases, suggesting that C. difficile can occupy a protective niche whereby antimicrobial therapy is ineffective. Biofilms represent such a potential niche. We sought to determine the role of biofilms in recurrent CDI (rCDI) and how the sessile community can affect C. difficile biofilm formation.
A triple stage chemostat model of the human colon was used to predict the efficacy of a simulated faecal microbiota transplantation (FMT) and two different dosing regimens of a spore consortium, SER-109, to prevent rCDI and to define a role for biofilms in rCDI. Planktonic and biofilm communities were individually analysed using culture-based techniques and bacterial taxonomic sequencing. Bile acid levels were monitored to investigate potential mechanisms of efficacy. A biofilm batch culture assay was used to investigate the influence of biofilm-associated microbiota on C. difficile biofilm formation.
Results show that FMT and a triple dose of SER-109 successfully prevented rCDI, potentially due to reducing the levels of primary bile acids through conversion to secondary bile acids. Despite the ability of microbiome therapies to prevent rCDI, they failed to eradicate C. difficile from the biofilm, suggesting a risk of future CDI. The biofilm-associated C. difficile was able to seed the planktonic phase, resulting in C. difficile germination and proliferation, which proved to be sufficient to induce CDI. Biofilm batch culture experiments indicate that commensal biofilm populations can reduce or increase C. difficile biofilm formation and growth, which required the presence of viable cells.
We conclude that biofilms provide a protective niche for C. difficile, which facilitates CDI recurrence, and that patients undergoing microbiome-based therapies potentially remain at risk of CDI with subsequent antibiotic use.