[xk_id]

> an increase in Bifidobacterium abundance. (Was not clear on a first read if that is necessarily always positive).

The total effect of a microbiome is not an additive function of the individual species. These species interact in highly complex ways. Some species might normally release factors that are detrimental to health, but their behaviour is suppressed by other species present in the flora. Therefore the individual species are not of therapeutic relevance; due to limitations in our understanding, each flora must be considered as a whole.

[CrHn3]

> Therefore the individual species are not of therapeutic relevance

Wanted to point out that this does not hold true for babies, where Bifidobacterium abundance generally does correlate with healthy microbiota and the strain B. infantis is relevant therapeutically and has evolved to metabolize milk sugars into short chain fatty acids.

[xk_id]

B infantis ferments lactose into lactate, which is afterwards utilised by lactate-consuming bacteria to kickstart butyrate production. In general, the infant gut is about striking a balance between lactate-producing and lactate-using bacteria. While bifidobacterium is usually dominant on the lactate-producing side, the same function can be (and is) fulfilled by other primary colonisers, such as Staphylococcus.

The point here is that individual strains are only "beneficial" in so far as they interact positively with others.