Frozen Stool: What About Stability and the Preservation of the Microbiome?


By: Dr. Shaina Cahill, Ph.D. (Director Medical Communications & Affairs)

Fecal microbiota transplantation (FMT) is the infusion of specially prepared stool material from a healthy donor(s) into the gut (intestinal tract) of a recipient to restore a healthy and stable microbial community and confer health benefits and/or treat a specific disease or symptom(s) 1–4(See our blog post to learn more about FMT

Several stool preparations can be utilized for FMT, including fresh, frozen, and lyophilized 5. Clinical research has demonstrated that frozen fecal preparations provide similar clinical efficacy in treating recurrent Clostridium difficile infections (rCDI) as fresh fecal preparations in FMT 6–16(See our blog post on fresh vs frozen stool preparationsto learn more).

A central question related to the use of frozen stool is the viability, engraftment, and efficacy of the gut microbiome over time during storage 7,17. Currently, there is contradictory information in the literature about bacterial viability and clinical effectiveness during long-term storage 18. A lack of comparative efficacy data over time and storage durations ranging from 6 months to 2 years, makes it difficult to make clear conclusions about the stability of frozen fecal preparations during long-term storage 8,17,19-24.

Studies have evaluated the effectiveness of frozen fecal preparations for FMT, with no significant differences noted in clinical outcomes despite large ranges in the storage time from 6 months to up to 12 months 7,17,18,20,23,24. Specifically, Allegretti et al. suggested that frozen storage duration for fecal preparations does not significantly impact clinical cure rate, as they reported that storage for less than 6 months showed an 83.8% clinical cure rate which was comparable in effectiveness to the reported 83.8% and 83.3% clinical cure rate reported at 6–12 months and more than 12 months of storage respectively18.

Another critical factor is the viability of gut microbiota after longer-term storage. Reygner et al. reported that both lyophilized and frozen fecal preparations showed good preservation in terms of viability and diversity of the main targeted bacterial groups over 12 months of storage (even 18 months in some cases), and donor microbiota profiles were also preserved 17. In support of these findings, studies have demonstrated the clinical efficacy of frozen fecal preparations, with confirmation of preserved and viable gut microbiota profiles and stable engraftment with frozen fecal preparations from 6 months up to 15 months 17,18,20,23,25,26.

While these findings are promising, two studies have reported reductions in the levels of viable bacteria in both frozen and lyophilized fecal preparations compared to fresh 27,28. While the changes in viable microbiota composition may be modest and research suggests no significant effects on FMT outcomes17,18,20,23,25,26, given that the mechanism of action of FMT is unknown, more clinical data on viability and engraftment of gut microbiota after long-term storage is of great importance. This is why we are currently doing our own research and stability studies to better understand the longevity of samples and to measure the viability of the stored microbiome.

At Novel Biome, we believe in the importance of the gut microbiome for overall health and the possibilities of fecal microbiota transplantation (FMT) to restore gut health and treat disease. Novel Biome focuses on FMT product manufacturing and supplying high-quality products, relying on our world-class donors to allow us to make a significant difference in the lives of many individuals, take our eligibility quiz to see if you can be a stool donor.

References:  1. Choi, H. H. & Cho, Y.-S. 2016, 2. Gupta, S. et al. 2021, 3. Ser, H.-L. et al. 2021, 4. Xu, M.-Q. 2015, 5. Gerardin, Y., et al. 2021, 6. Tang, G. et al. 2017, 7. Ramai, D. et al. 2019, 8. Fadda, H. M. 2020, 9. Hamilton, M. J. et al. 2012, 10. Ianiro, G. et al. 2018, 11. Kao, D. et al. 2017, 12. Lee, C. H. et al. 2016, 13. Satokari, R. et al. 2015, 14. Youngster, I. et al. 2014, 15. Quraishi, M. N. et al. 2017, 16. Reigadas, E. et al. 2020, 17. Reygner, J. et al. 2020, 18. Allegretti, J. R. et al. 2020, 19. Terveer, E. M. et al. 2017, 20. Jiang, Z.-D. et al. 2017, 21. McBeth, A. & Dobner, P. 2019, 22. Mullish, B. H. et al. 2018, 23. Staley, C. et al. 2017, 24. Youngster, I. et al. 2016, 25. Costello, S. P. et al. 2015, 26. Hamilton, M. J. et al. 2013, 37. Jiang, Z.-D. et al. 2018, 28. Papanicolas, L. E. et al. 2019.

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