In this contribution, GMFH board member Mary Ellen Sanders analyzes one of our recent website selections:  Veiga et al. (2014) Changes of the human gut microbiome induced by a fermented milk product.

Probiotics are a promising means to manipulate the microbiome, but there is little evidence that they can do this by changing the microbiota composition. Yes, the genus or species of the probiotic are transiently increased, but there is little evidence that probiotics can reshape a microbial community.

Veiga et al. (2014) suggest that the lack of such evidence may be due to poor resolution of the phylogenetic tools used to date. Using updated methods, they detected species-level changes after feeding female IBS subjects yogurt containing Bifidobacterium animalis subsp. lactis, Lactococcus lactis, and the yogurt starter bacteria. The observed changes were increases of 4 unknown species (MGS126, MGS203, MGS106, MGS109) and Bifidobacterium dentium, and reductions of Parabacteroides distasonis, Bilophila wadsworthia (an opportunistic pathogen) and Clostridium sp. HGF_2 . In subjects consuming the acidified milk control product, Haemophilus parainfluenzae and a 5th unknown species (MGS204) were reduced. In addition, yogurt increased short chain fatty acids. Applying functional genomic tools, the metabolic pathways of the unknown species can be elucidated, providing insight into what roles these microbes might play.

This work shows that dietary microbes lead to microbiota changes in IBS subjects. The authors suggest that these changes may ameliorate symptoms through improved homeostasis of gut microbiota and their functions through cross feeding between ingested bacteria and resident ones.

The ability of dietary microbes to promote stability of the gut microbial communities is an intriguing hypothesis. Although the ideal composition of a healthy gut microbial community is not known, a reasonable argument could be made that a useful characteristic of a probiotic in a healthy person is to maintain microbiota stability – either through promotion of resilience so that a potential perturbation has less of an effect, or through facilitating a return of a perturbed microbial community to normal. Such a homeostatic function could also be brought to bear after correction of some deficiency in a microbial community (as occurs with fecal microbial transplant or other microbial interventions), with the aim of promoting stability of the newly established, healthier community.

The Veiga et al. (2014) paper proves that one probiotic yogurt can impact the gut microbial community; additional studies targeting the promotion of stability of gut microbial communities through ingestion of probiotic yogurt would be of great interest.