Clostridium innocuum is increasingly detected in patients with Clostridioides difficile infection (CDI), particularly following vancomycin treatment, and is associated with delayed clinical recovery and poor outcomes. Although C. innocuum lacks classical toxins, its lipopolysaccharide-like cytotoxic activity and emerging pathogenic role remain poorly understood. In this study, we conducted co-infection models to explore the interactions between toxigenic C. difficile and C. innocuum in human intestinal epithelial cells. Our results showed that C. innocuum alone exhibited minimal cytotoxicity; however, its presence significantly enhanced cell death and barrier disruption during co-infection with toxigenic C. difficile. Pre-infection with toxigenic C. difficile promoted C. innocuum translocation across epithelial monolayers, indicating that toxin-mediated barrier damage facilitates deeper colonization. Co-infection further activated p53-mediated stress signaling and altered the BAX/BCL-2 ratio, driving apoptosis through PARP1 activation. Notably, the organism's intrinsic vancomycin resistance enables its survival and expansion during CDI treatment, fostering its emergence as a pathobiont. Our results demonstrate that toxigenic C. difficile facilitates C. innocuum epithelial invasion and exacerbates host cell damage through synergistic interactions. These findings highlight C. innocuum as a clinically relevant pathobiont, emphasizing the need for improved diagnostics and targeted strategies in CDI management.
Kuo et al. (Sat,) studied this question.