Clostridioides difficile is an opportunistic bacterium that causes diarrhoea in hospitalised patients undergoing antibiotic treatment through the action of three well-known toxins identified over 30 years ago. The epidemiology of C. difficile infections (CDI) has changed in the last decades, revealing its One-Health nature and diversity in the repertoire of toxins and virulence factors produced by the bacterium’s distinct evolutionary lineages. Excitingly, our group has discovered a novel virulence factor produced by C. difficile, named CdV (C. difficile virulence factor), which belongs to a growing family of large multiprotein complexes capable of injecting effectors into host cells. Our work is the first to identify and investigate this factor in the Clostridia and one of the few studies addressing the contribution of this group of virulence factors to mammalian enteric infections.
By screening close to 20,000 C. difficile genomes, we have identified the locus encoding the cdv genes in five phylogenetic clades, mainly deriving from production animals and environmental samples. This locus is also present in strains isolated from human samples, suggesting a possible zoonotic origin. Our systematic approach to understanding the evolution of this factor revealed that cdv-like loci exist in other diverse bacterial species and are thus likely to be transferred to new bacterial hosts in shared niches in the environment and animals. To explore the role of CdV in CDI, we inactivated this virulence factor in a strain lacking the known C. difficile toxins. Using a combination of techniques, we found that CdV modulates the response to CDI by dampening the murine colonic immune response and the expression of genes involved in cellular stress and by changing the abundance of circulating metabolites. These physiological changes occurred without damage and diarrhoea during acute infection, suggesting that CdV might be a camouflaging effector, stealthily manipulating host responses essential to guarding homeostasis.