# Effect of Supplementation with Lactobacillus reuteri SGL 01 in Lactating Women on Breast Milk and Neonatal Gut Microbiota: An Exploratory, Randomized, Open-Label Clinical Trial

## TL;DR

This study explores how giving Lactobacillus reuteri to lactating mothers affects breast milk and their babies' gut microbes, finding changes in the infants' gut bacteria.

## Contribution

The study is the first to show that maternal L. reuteri supplementation indirectly affects neonatal gut microbiota without altering breast milk composition.

## Key findings

- Neonates of supplemented mothers had increased Bifidobacterium, Lactobacillus, and Clostridium in their feces.
- Breast milk microbiota composition remained unchanged by maternal L. reuteri supplementation.
- Control group infants showed a slight reduction in Clostridium spp.

## Abstract

Background/Objectives: Early-life gut colonization is crucial for immune system development and metabolic programming. Lactobacillus reuteri has been investigated for its capacity to modulate neonatal gut microbiota, but evidence regarding maternal supplementation during lactation remains limited. This study aimed to evaluate the effect of maternal supplementation with L. reuteri SGL 01 on the microbial composition of breast milk and neonatal feces over the first month of life. Methods: This is an exploratory, prospective, open-label randomized clinical trial. Lactating mothers of full-term and exclusively breastfed infants were randomized to receive either daily L. reuteri SGL 01 (1 × 109 CFU) for 30 days or no supplementation. Quantitative real-time PCR was used to assess Bifidobacterium spp., Lactobacillus spp., Clostridium spp., and the Bacteroides fragilis group in maternal milk and neonatal feces at baseline (T0) and after 30 days (T1). Results: Twenty-seven mother–infant dyads completed the study (15 supplemented, 12 controls). No significant changes in breast milk microbiota composition were observed across any of the bacterial taxa following maternal supplementation. In contrast, neonatal fecal samples from the supplemented group showed significant increases in Bifidobacterium spp. (p < 0.001), Lactobacillus spp. (p = 0.029), and Clostridium spp. (p = 0.003) at T1. No significant microbial changes were observed in the control group, except for a slight reduction in Clostridium spp. (p = 0.046). Conclusions: Maternal supplementation with L. reuteri SGL 01 did not modify breast milk microbiota but was associated with a modulation of neonatal gut colonization, including an increased abundance of beneficial taxa such as Bifidobacterium, suggesting potential indirect maternal-to-infant microbial effects.