A popular misconception is that probiotic microbes colonise the gut on a durable/permanent basis. This is simply not true. Probiotic microbes tend to persist in the gut for several days to a week. An exception to this can be bifidobacteria given in early infancy.
There is some limited evidence that these may become part of the gut flora in the infant on a longer-term basis. But for the overwhelming majority of people the persistence of supplemented probiotic microbes in the gut extends out to a maximum of about a week.
Most freeze-dried probiotic products have a seemingly impressive list of microbes listed on the label. The assertion is then made that the product is ‘multi-strain’. While this is true in a very limited sense, it is really sidestepping the whole reason why a consumer would want a multi-strain product in the first place.
In the real world, microbes are never alone, they never live only among their own species/strain. Microbes are always in vast communities with friends and competitors engaged in an eternal struggle for survival. Very early in the development of probiotics, it was observed that cultures containing several different microbes tended to outperform cultures containing only a single strain. These observations were generally on live active cultures, not just blends of various powdered freeze-dried bacteria.