Randomized, placebo-controlled trial reveals the impact of dose and timing of Bifidobacterium infantis probiotic supplementation on breastfed infants' gut microbiome.

Fecal B. infantis levels were significantly higher in all supplement groups compared with placebo on both day 28 and day 63.

• Study enrolled 40 exclusively breastfed infants aged 2-4 months in equal allocation across four groups.
• Groups received 0 CFU/day (placebo), 4.0 × 10^9 CFU/day (low), 8.0 × 10^9 CFU/day (medium), or 1.8 × 10^10 CFU/day (high) B. infantis EVC001.
• Supplementation was administered for 28 consecutive days beginning on study day 8.
• Stool samples were collected on study days 7, 10, 14, 21, 28, 35, 42, and 63.
• Day 63 represents approximately 1 month after the end of supplementation, indicating persistent colonization.

Fecal B. infantis levels were significantly higher in all probiotic-supplemented infants compared with their own baseline on day 28.

• This finding applied to infants in the low, medium, and high dose groups.
• Baseline was measured on study day 7, before supplementation began on day 8.
• The effect was observed regardless of dose level.

The abundance of fecal Bifidobacteriaceae significantly increased nearly 2-fold in response to B. infantis EVC001 supplementation.

• This increase in Bifidobacteriaceae family-level abundance was observed across supplementation groups.
• The effect extended beyond just B. infantis to the broader Bifidobacteriaceae family.
• This increase was observed in 2-4 month old infants whose gut microbiomes are typically transitioning toward stability and maturity.

B. infantis EVC001 colonization persisted for at least 1 month post-supplementation in 2-4 month old exclusively breastfed infants.

• Probiotic supplementation lasted 28 consecutive days (days 8-35 of the study).
• Elevated fecal B. infantis levels were still detected on day 63, which is approximately 28 days after supplementation ended.
• This persistence was observed regardless of dose (low, medium, or high).
• This is described as the first study to demonstrate colonization in older infants whose gut microbiomes are typically more stable than newborns.

A dysfunctional gut microbiome lacking Bifidobacterium dominance has become increasingly common in infants born in high-income countries.

• Bifidobacterium strains no longer dominate the gut microbiome in many infants in high-income countries.
• Previous studies had only demonstrated B. infantis probiotic restoration of the gut microbiome in breastfed newborns, not older infants.
• No studies prior to this one had demonstrated this effect in older breastfed infants whose gut microbiomes are transitioning toward stability and maturity.

This was a 9-week randomized, placebo-controlled trial with four treatment arms in equal allocation.

• The trial was registered at clinicaltrials.gov as NCT03476447.
• Total sample size was n = 40 exclusively breastfed infants aged 2-4 months.
• Four groups: placebo (0 CFU/day), low (4.0 × 10^9 CFU/day), medium (8.0 × 10^9 CFU/day), and high (1.8 × 10^10 CFU/day).
• Eight stool sample collection timepoints: study days 7, 10, 14, 21, 28, 35, 42, and 63.
• The probiotic used was B. infantis EVC001 administered for 28 consecutive days.