Metabolic and pathogenic implications of sialic acid utilization in Clostridioides difficile infection

Clostridioides difficile infection is a growing public health concern, marked by high recurrence rates and substantial clinical and economic burden. While gut microbiota disruption is a well-established driver of C. difficile infection (CDI), recent studies suggest that sialic acid (Sia), a terminal monosaccharide found on host glycoconjugates, may contribute to key aspects of C. difficile colonization and persistence. In this review, we explore how C. difficile interacts with Sia in the gut environment. Genomic analyses reveal that while the bacterium lacks sialidase activity and de novo Sia synthesis, it can catabolize free N-acetylneuraminic acid (Neu5Ac), relying on other microbes to liberate it from host glycans. We examine evidence linking Sia availability to nutrient acquisition, toxin binding, mucosal interactions, and microbial competition, particularly under dysbiotic or inflamed conditions. Additionally, we review emerging therapeutic approaches, including microbiota-based interventions and engineered probiotics, that may influence Sia dynamics or exploit them to suppress C. difficile. Although the role of Sia in CDI remains incompletely understood, growing evidence points to its relevance in shaping host-microbe and microbe-microbe interactions. We highlight current knowledge gaps and propose directions for future research to clarify the functional importance of Sia in C. difficile pathogenesis and therapy.