Genomic and phenotypic insight into Clostridioides difficile RT027 isolates from China reveals diverse virulence...

Clostridioides difficile (C. difficile) ribotype 027 (RT027) has caused severe outbreaks in North America and Europe over the past 20 years. However, RT027 infections are rare in Asia, particularly in China, with limited severe cases. To clarify its molecular and phenotypic features, we investigated 11 RT027 isolates collected from Shandong, China. Whole-genome sequencing, comparative transcriptomics, CRISPR-Cas analysis, and pan-genome profiling were combined with phenotypic assays of toxin production, sporulation, antimicrobial resistance, and motility. Evolutionary analysis demonstrated that isolates from China clearly diverged from the FQR2 lineage and were phylogenetically closer to FQR1, forming a distinct sublineage. All isolates from Shandong, China encoded a complete tcd and cdt locus and harboured rifamycin and aminoglycoside resistance genes. However, transcriptomic profiling demonstrated significantly reduced expression of binary toxin genes (cdtAB, cdtR), decreased spo0A transcription, and downregulation of flagellar pathways. Phenotypic assays confirmed impaired sporulation, motility and cytotoxicity, while TcdB production and adhesion was comparable to reference strains. CRISPR-Cas elements were conserved but showed reduced transcriptional activity, suggesting diminished host-pathogen interactions. The pan-genome revealed high genomic conservation, consistent with limited functional diversity. Together, these data indicate that RT027 isolates circulating in China possess unique evolutionary trajectories and attenuated virulence traits, helping to explain the rarity of severe RT027 infections in Asia. These findings provide important insights into the regional epidemiology of C. difficile and inform strategies for diagnosis, treatment, and prevention.