As I alluded to, success or failure of FMT is not simply just about the transfer of beneficial bacteria. There are far more factors involved in it being effective or not, and that part of the science is still very much a work in progress.
https://journals.sagepub.com/doi/10.1177/1756284820946904
Mechanisms underpinning the efficacy of faecal microbiota transplantation in treating gastrointestinal disease (2020)
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6236173/
The need to move away from fecal transplant towards targeted, refined microbiome therapy
[ The mechanisms behind FMT’s efficacy are largely unknown (
2), which can prevent the development of a targeted, refined microbiome based therapy. The contents of FMT are complex, and include both live and dead bacteria as well as non-bacterial components such as viruses, bile acids and proteins (
2). It is not known if some, or all of these components are necessary for the clinical efficacy of FMT. When considering the gut microbiome, it is vital to consider not only the bacteria, but also the viruses (virome), the fungal elements (mycobiome) and many small molecules, such as bile acids, and short chain fatty acids (SCFAs). These factors may be contributing to, or perpetuating gut dysbiosis, a hallmark of
C.
difficile pathogenesis. ]
https://journals.sagepub.com/doi/10.1177/1756284820946904
Mechanisms underpinning the efficacy of faecal microbiota transplantation in treating gastrointestinal disease (2020)