While evidence of the benefits of Lactobacillus rhamnosus GG (LGG) for intestinal problems, respiratory infections and eczema have previously been identified by scientists, the key mechanism underlying this effect has been unclear.
The University of Maryland scientists, led by Claire Fraser, analysed gut bacteria before and after administering LGG. They found that it had led to increases in several genes that foster different species of gut bacteria, including Bacteroides, Eubacterium, Faecalibacterium, Bifidobacterium and Streptococcus.
"This is a new idea - that some probiotics may work by affecting the overall ecosystem of the gut," said Fraser. "Previously we tended to think that LGG and other probiotics worked directly on the host. I think this finding has many exciting implications."
12 male and female patients aged between 65 and 80 years were recruited to take part in the study. They took colony-forming units of LGG probiotic twice a day for 28 days, and the scientists took faecal samples before probiotic consumption, on day 28 and one month after stopping.
Using metagenomics analysis Fraser et al. then took a series of measurements of the resident microbes to evaluate the changes on the structure and function of the resident microbiota - nearly 300,000 sequence readings from bacterial rRNA genes
According to the study ”LGG may promote interactions between key constituents of the microbiota and the host [tissue].
“These results provide evidence for the discrete functional effects imparted by a specific single-organism probiotic and challenge the prevailing notion that probiotics substantially modify the resident microbiota within nondiseased individuals in an appreciable fashion.”
The researchers found increased expression of Bacteroides, Eubacterium, Faecalibacterium, Bifidobacterium and Streptococcus but call for further deep sequencing of community microbiota to determine whether rare bacteria strains are also impacted.
Dean Albert Reece, vice president for Medical Affairs at the University of Maryland said: “Dr Fraser’s study… will help advance a rapidly emerging research area."
Source: mBio Journal
First published online 14 April 2015, doi: 10.1128/mBio.00231-1514
"Functional Dynamics of the Gut Microbiome in Elderly People during Probiotic Consumption"
Authors: A. Brady, C. Fraser et al.