Long-term stability and efficacy of frozen fecal microbiota transplant (FMT) product at 24 months

Freezing donor fecal microbiota has improved fecal microbiota transplantation (FMT) for recurrent C. difficile infection (CDI), achieving short-term effectiveness similar to fresh-samples. Research shows frozen fecal matter remains effective for up to 12-months at -80 °C. Objective: To assess how long-term-freezing and thawing affect the viability, microbial composition, and clinical efficacy of frozen-stools for FMT. Methods: Stool samples from three donors were processed into 18 aliquots, thawed at intervals over two years, and analyzed for cell viability and microbial load. Microbiota composition was assessed through 16S-sequencing, with diversity evaluated using the Shannon-index and Principal-Coordinates-Analysis based on Bray-Curtis-distance (α/β-diversity). The same donors provided fecal material for a total of 23 FMT procedures, including 15 for CDI and 8 off-label. Results: We found that donor stools frozen for two years contained viable bacteria comparable to fresh samples, with anaerobic and aerobic species remaining viable for 24 months. Despite a reduction in colony-forming-units, FMT was successful in 71.4 % and 100 % of the cases at one year and at the end of follow-up, respectively. Most bacterial changes occurred among anaerobic species (Blautia producta and Bifidobacterium adolescentis), increasing post-thawing. Notably, specific taxa, (C. aerofaciens and Erysipelotrichaceae_Cc115), showed significant unexplained increase. Conclusion: Long-term-stool-storage enhances FMT accessibility without compromising its success, despite taxonomic changes after 24 months.