Not every type of bacteria in your gut microbiome is known and/or able to be grown in culture.
As per your question regarding pro-biotics, some bacteria such as Lactobacilli can be dried and remain viable when reintroduced to a liquid medium.
Re:Sell your poop for $13,000 per year
by abandonliberty on Tuesday February 03, 2015 @12:17PM
(#8991616)
Yes - we can only culture a very small minority of wild bacteria.
For example, the recent antibiotic discovery that made the news came from learning how to culture soil bacteria. No, we didn't learn what it needs. We just grew it in it's natural environment: dirt.
https://news.ycombinator.com/item?id=8852487
Revolutionary. (seriously).
I was wondering that myself. One guess- the proportions are important and they don't know what culture medium to use. The gut is a complex environment. What if they grow it in a lab and some unknown minor microbe is selected out?
On the other hand, I bet they're working on it.
Anaerobic bacteria are incredibly difficult to culture, especially if the specie is one that doesn't spore or last long in aerobic conditions. Those are most likely what are in the probiotic pills, but I do not know and am only speculating.
On a related note, how can the bacteria survive in "pro-biotic" pills that you can buy? I'm suspicious.