[Screening and phenotypic characterization of Nontoxigenic Clostridioides difficile for intervention in C. difficile infection].

Objective: To identify candidate strains of Nontoxigenic Clostridioides difficile (NTCD) with potential for intervention in Clostridioides difficile infection (CDI) and analyze their phenotypic characteristics. Methods: A total of 713 Clostridioides difficile strains from various sources were systematically collected nationwide between 2015 and 2023. This included 649 strains isolated from human fecal samples and 64 strains isolated from the fecal samples of farmed animals. NTCD strains were preliminarily screened through toxin gene detection and antibiotic sensitivity test, and then NTCD candidate strains with potential for intervention in CDI were screened by a series of in vitro experiments, including MLST, sporulation, germination, adhesion, motility, and biofilm formation ability. Ultimately, the virulence genes and antimicrobial resistance genes of the candidate strains were comprehensively analyzed to rigorously assess their safety profiles. Results: Among 713 strains of C. difficile from different sources, 10 strains were initially screened out, which were non-toxin-producing and sensitive to antibiotics. MLST showed that seven strains were from the Clade1 branch and three strains were of a novel type. The results of sporulation and germination showed that SD59, SD178, SJZ17, and WZ142 had stronger sporulation and germination abilities. The adhesion of 10 strains was high, and the adhesion rate was between 72.93% and 99.32%. The motility of all strains was different, and the motility of SD178, SD59 and SJZ17 was stronger. The biofilm-forming ability of all strains was weak. SD59, SD178 and SJZ17 carried a limited number of virulence and resistance genes, thereby posing a relatively low safety risk. Conclusion: Three NTCD strains are successfully selected as potential effective NTCD strains to interfere with CDI.