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

Background: 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.