Gut microbiome profiles in Clostridioides difficile-positive and C. difficile-negative antibiotic-associated diarrhea

Introduction Antibiotic-associated diarrhea (AAD) is a common complication of antibiotic therapy. Although Clostridioides difficile infection (CDI) is the leading cause of AAD, many patients develop AAD without detectable C. difficile . We investigated differences in the gut microbiota between C. difficile -positive (CDAD) and C. difficile -negative (non-CDAD) AAD. Methods In this retrospective, single-center study, we analyzed stool samples collected in 2019 from 42 patients with AAD (19 with CDAD and 23 with non-CDAD) and 21 healthy controls using 16S rRNA gene-based microbiome analysis. Microbial diversity, community composition, and discriminatory taxa were evaluated using alpha diversity analysis, Bray–Curtis principal coordinates analysis (PCoA), and linear discriminant analysis effect size (LEfSe). Results Both the CDAD and non-CDAD groups exhibited significantly reduced microbial richness and diversity compared with those of the healthy controls (all P < 0.01), whereas no significant differences in alpha diversity were observed between the two AAD groups. Beta diversity analysis demonstrated distinct clustering of both AAD groups from the healthy controls, but not between the CDAD and non-CDAD groups. Both AAD groups were depleted of short-chain fatty acid-producing genera, including Faecalibacterium , Roseburia , Agathobacter , Anaerostipes , Dorea , and Phascolarctobacterium . LEfSe identified distinct species-level discriminatory taxa in each group. The non-CDAD group was enriched in the Enterococcus faecium group, Enterococcus faecalis , the Enterobacteriaceae group, Klebsiella sp. FWNZ, and Alistipes onderdonkii , whereas the CDAD group was characterized by enrichment of the C. difficile group, Bifidobacterium scardovii , Bacteroides thetaiotaomicron , Ruminococcus gnavus , Clostridium ramosum , and Flavonifractor plautii . Discussion Although CDAD and non-CDAD exhibited comparable reductions in overall gut microbial diversity, each condition was associated with distinct taxonomic signatures. These findings provide insights into the microbial dysbiosis associated with AAD and identify candidate microbial signatures that warrant further validation in independent cohorts.