Hi b_jim,
I have been doing a lot research on gut bacteria. From what I've read, the gut ecosystem is fully developed by the age of 4 years old and the bacterial strains are then not easily changed from that point.
I guarantee you that most probiotics reach the gut intact, I can feel the effects on the day after I take them. The real question is whether the supplement has been stored badly by the seller and the bacteria have died. The strain of bacteria is also very important, people think buying a probiotic with 30 strains is better than a single strain product but those 30 strains might be taken from a pig's gut and not be very effective in humans or those strains could not be well studied or they might interfere with each other. The BB536 I take is from a human gut, it was compared alongside a number of other human bacteria and found to have the best beneficial properties for human health.
I did a lot of research into microbiota transplantation (FMT), it seems like the effects for that might be temporary. I wrote a list of issues I have with FMT in this thread a while ago, there's a lot of problems they need to fix before I would ever try it.
The psychobiotics, as I understand it, refers to probiotics that can improve mood. I have a few probiotics that claim to improve mood called "Zenflore" and "Florassist Mood", they seem to all be strains of Bifidobacterium Longum. My BB536 probiotic is also a strain of B. Longum and seems to help my mood. I do think there is a link between gut dysbiosis and mental disorders like depression.
My experience of probiotics is that they can shift your bacteria in a positive direction but they do not colonise the gut permanently so they need to be supplemented regularly, the main difficulty is finding one that is effective for your particular gut. I have taken prebiotics like FOS, GOS and inulin but it feels like these feed the bad bacteria too. I also react badly to fermented foods and I think this may be because of the large amounts of fungi they contain, it is suggested that anyone with SIBO should avoid fermented foods.
To put my experiences simply, I have been seriously ill and tried everything possible to improve my gut (excluding FMT). Finding an effective single-strain probiotic like BB536 appears to have gradually corrected my gut imbalance and I will probably have to take it for life, which is fine by me despite the cost. I think I was on the very extreme of gut dysbiosis, pretty much anything I consumed would trigger severe issues resembling autoimmune disease and I suppose that is because I don't have much good bacteria left. I seemed to tolerate BB536 so I kept upping my dosage and now I can eat most foods. I still have trouble with fermented foods, possibly because they contain large amounts of bacteria and yeast which undermines the effects of the BB536.
When the providers of FMT fix the many issues with the procedure, I will gladly consider trying it. I still get the impression that the human gut doesn't easily allow new strains to colonise permanently so maybe the effects of FMT wear off after 2 months. I think in the future they will just put the FMT bacteria in a capsule and people will take it everyday like a multivitamin, it will be a 1000 strain probiotic. The other future technology with hopefully be Human Milk Oligosaccharides, these are the natural prebiotics found in human breast milk that help babies to build a gut ecosystem.