Probiotic bacteria consumed in a yogurt may not change the host’s gut populations, but they do influence carbohydrate metabolism by the resident microbes, according to an ‘elegant’ new study using identical twins and germ-free mice.
Probiotics in a yogurt were not found to colonize the gut microflora when studied in identical twins, but additional study in mice revealed that ingestion of the probiotic bacteria produced a change in many metabolic pathways, particularly those related to carbohydrate metabolism.
Researchers led by Dr Jeffrey Gordon at the Washington University School of Medicine, St. Louis, published their results yesterday in Science Translational Medicine.
In an accompanying perspective article the study was described as “elegant” by Jordan Bisanz and Gregor Reid from the Lawson Health Research Institute at the University of Western Ontario.
Dr Gordon and his team have made a habit of advancing our understanding of gut microbe populations and their interactions with their hosts. In 2006, the St Louis-based researchers reported in Nature (Vol. 444, pp. 1022-1023, 1027-1031) that microbial populations in the gut are different between obese and lean people, and that when the obese people lost weight their microflora reverted back to that observed in a lean person, suggesting that obesity may have a microbial component.
“One of the questions that this field is asking is what are the effects of these organisms on individuals,” said Dr Gordon in an audio podcast with Science Translational Medicine .
“Can we create a discovery pipeline where we can analyze their effects under highly controlled conditions – more controlled than we can achieve with human studies – and having interrogated those models, can we translate the information to humans to guide clinical trials, and gain a greater degree of insight about their effects?”
And that is what the researchers appear to have created. According to Bisanz and Reid, “a valuable roadmap has now been produced to guide future research on how exogenous organisms affect the host – and specifically its microbiome”.
In an email to NutraIngredients-USA, Prof Reid added: "The study is important as it tests a probiotic food in humans then investigates the mechanisms of action using a variety of state-of-the-art methods. The researchers then create a reduced microbiota in an animal and show that the effects of the probiotic can to some extent be mimicked."
Dr Gordon and his team examined the potential of four months of consuming a commercial yogurt containing Bifidobacterium animalis subsp. lactis, two strains of Lactobacillus delbrueckii subsp. bulgaricus, Streptococcus thermophilis, and Lactococcus lactis subsp. cremoris, in seven pairs of female twins in their 20s and 30s. Dr Gordon has not named the product to avoid being seen as endorsing it.
The researchers also tested the effects of the yogurt in gnotobiotic mice, or mice that were completely germ-free except for the 15 specially introduced strains of bacteria that are present in the human gut.
Results showed that, in both mice and humans, the probiotic yogurt did not modify the composition of the gut microbial communities.
However, further analysis of using genome sequencing, and transcriptomic and metabolomic analyses, revealed a change in marked changes in numerous metabolic pathways, particularly those related to the processing of carbohydrates.
According to Bisanz and Reid, “a real strength of [Dr Gordon’s] study is that ingestion of a fermented milk product, essentially a commercial probiotic yogurt, was monitored by having the microbial transcriptional responses from the animal model acting as biomarkers for interrogation of the metatranscriptome data sets of the human twins.
“The apparent stability of the twins’ gut microbiota, despite a twice daily intake of the fermented milk product containing bifidobacteria and lactic acid-producing bacteria, demonstrates the remarkable ability of the host’s microbes to withstand the arrival of new strains of bacteria.”
Dr Gordon and his co-workers note that his team’s experimental model could be used to identify biomarkers and other ‘mediators of the effects of existing or new probiotic strains’
The model may also help scientists identify potential new prebiotics that could also modify the metabolic effects of probiotic species.
Bisanz and Reid added that the “incredible precision and thoroughness of [Dr Gordon’s] study will not be easy to duplicate, but they have certainly laid a valuable pathway for others to follow.”
Source: Science Translational Medicine
26 October 2011, Volume 3, Issue 106, 106ra106
“The Impact of a Consortium of Fermented Milk Strains on the Gut Microbiome of Gnotobiotic Mice and Monozygotic Twins"
Authors: N.P. McNulty, T. Yatsunenko; A. Hsiao, et al.