*4.3. Fecal Microbiota Transplantation in Clostridium difficile Infection*

More recent work has studied fecal microbiota transplantation (FMT) for recurrent *Clostridium difficile* infection.

Patients with severe CDI refractory to traditional antibiotic treatment have had success with FMT, which restores colon homeostasis by reintroducing bacteria from healthy donor stool. The success rate for FMT is greater than 90% for those who had recurrent CDI, but the mechanism behind this treatment is partially unknown [59].

Successful fecal microbiota transplantation is correlated with a dysbiosis resolution by the replenishment of *Roseburia* and *Bacteroidetes*, which are also involved in butyrate production. After fecal transplantation, studies reported the presence of an increase in richness and diversity, an eradication of *Proteobacteria* species, and a restoration of *Firmicutes* and *Bacteroidetes* species [60].

They also found that the patients' gut communities were completely restored within three days following fecal transplantation, with stability in species for at least four months and indistinguishable from that of the donor [61].

Following FMT, *Bacteroidetes* increased and *Proteobacteria* decreased. Some others observed protective microbial taxa are *Alistipes, Ruminococcaceae, Lachnospiraceae, Peptostreptococcaceae,* and *Verrucomicrobiaceae*. All the species are negatively correlated to *C. difficile* colonization [62] (Figure 4).

This is an emblematic example of how by being able to re-establish that fundamental relationship between the host and gut microbiota, one of its most important functions, namely that of immune regulation, can be recovered.

All these new discoveries undoubtedly make it one of the most promising and steadily growing fields in all of medicine.

**Figure 4.** Major changes in the gut microbiota following fecal microbiota transplantation (FMT) [60,62]. After the procedure, there is an increase in the richness and diversity of the microbiome and the restoration of *Bacteroidetes* and *Roseburia*, which are involved in butyrate production. There is also restoration of *Firmicutes* and other protective microbial taxa such as *Alistipes*, *Ruminococcaceae*, *Lachnospiraceae*, *Peptostreptococcaceae*, and *Verrucomicrobiaceae*. At the same time, an important decrease in Proteobacteria occurs.
