Bacteria from fermented foods will not implant either. But that is not to say that these bateria are not beneficial. They just need to be ingested on a regular basis. I do not think that fecal matter fom a baby would be ideal since their intestinal flora is still evolving and is somewhat different bacteria composition than a healthy adult. I think the ideal fecal donor would be a healthy adult who was breast fed as a baby. For some reason probiotics cultured in the lab have lost their ability to colonize, but I can not tell you why this is.