Modulatory effect of three probiotic strains on infants' gut microbial composition and immunological parameters on a placebo-controlled, double-blind, randomised study.

The gut microbiota plays a crucial role in gastrointestinal health. Current use of probiotics is aimed at modulating the bacterial gut composition to alleviate specific diseases. The safety and tolerance of three probiotic strains (Bifidobacterium longum subsp. infantis R0033, Lactobacillus helveticus R0052 and Bifidobacterium bifidum R0071) has recently been described. The objective of the present study was to analyse the microbiological composition and immunological parameters of faecal samples obtained from healthy infants from 3 to 12 months of age after receiving either one of the three probiotic strains or placebo for 8 weeks. 16S ribosomal RNA gene sequencing and multiplexing technology was used for analysis. Faecal sample analysis showed that the most abundant genus in all four groups of infants pre- and post-intervention was Bifidobacterium, representing approximately 50% of the sequences. After the intervention period the microbial composition of faecal samples in the probiotic groups did not display notable changes. In contrast, a decrease in different Bifidobacterium species, such as B. bifidum and Bifidobacterium breve and an increase in Bacteroides, Blautia, Clostridium, Coprococcus and Faecalibacterium genera was observed in the placebo group. The analysis of a wide range of immune factors in faecal samples suggests a modulatory effect by these three probiotic strains during the intervention period. The anti-inflammatory ratio interleukin (IL)-10/IL-12 increased at the end of the intervention period in the B. infantis R0033 group while the TNF-α/IL-10 ratio increased in the L. helveticus R0052 group. The decrease of the IL-10/IL-12 ratio together with the increase of the tumour necrosis factor alpha (TNF-α)/IL-10 ratio demonstrated a pro-inflammatory profile in the placebo group. In conclusion, the species profile of the microbiome observed in all three probiotic groups resembled that of a younger infant, similar to an unweaned infant, when compared to the placebo group which may also be related with an anti-inflammatory effect.