The microbiome in the animal gut is susceptible to a variety of conditions:

Transient osmotic perturbation causes long-term alteration to the gut microbiota, Tropini et al 2018

Impact of antibiotics on the human microbiome and consequences for host health, Patangia et al 2022

Bactrim (sulfamethoxazole and trimethoprim) is a combination antibiotic. Is there a danger of making the gut microbiota less diverse? That would be detrimental to health in the long term.

Impact of Long-Term Low Dose Antibiotic Prophylaxis on Gut Microbiota in Children, Akagawa et al 2020. Sci-hub doesn't have this article and I don't know what exactly is “low dose” or “long term”.

https://academic.oup.com/ajcn/article/73/2/399s/4737569
“ Should it become desirable to permanently colonize the human intestinal tract with an exogenous probiotic, it is reasonable to suggest that a human-specific probiotic with potent intestinal mucosal cell adhesion properties be chosen. Selection of such strains on the basis of this criterion may be insufficient. It may be necessary to culture surgical or biopsy specimens to select suitable probiotic strains. “
” An ideal probiotic would be one that can survive passage through the gastrointestinal tract, [and] establish itself permanently in the small intestine and colon… ”

Many probiotics do survive stomach acid, and the bile salts of the small intestine, they just don't adhere to the mucosal lining of the large intestine, to take up residence with the existing bacteria. I imagine this is true of all existing probiotics on the market? Would a company sell a probiotic that only needs to be taken once?

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3337120/
Germ free mice, fed all 10 strains of *human* bacteria, did not retain all 10 strains, rather at most 3. I guess because bacteria compete with each other. The best method they found to successfully build up the full array of bacteria, was to feed individual germ free mice a single bacteria, and then mix the mice together in the same cage (since like dogs, they eat each other's poop). The idea is, that the individual human gut bacteria needed to first adapt to living in the mice. Once adapted, they could easily gain hold in other mice as well.
“ Moreover, GF animals introduced to these isolators on day 56 of the study, quickly acquired a similar bacterial community to that of the donor animals, suggesting that the transferred microbial community had achieved a significant level of stability and adaptation to the host gut environment. “
So, once the bacteria had adapted/evolved to live in mice, then they could all settle in to a new mouse, all at once, unlike before, where at mot 3 strains survived.

So are companies selling strains of probiotics that are good at colonizing a human gut? Would that be a good monetary investment for the medical industry?