This prospective, randomised, double blind, placebo-controlled study identified factors affecting the prevalence of Lactobacillus reuteri in the faeces and breast milk of 232 mothers with a history of atopic disease, and in the faeces of their babies after oral supplementation with Lactobacillus reuteri ATCC 55730.

Women were randomly assigned to take either Lactobacillus reuteri or placebo for the last 4 weeks of their pregnancy. Their babies continued with the same study product from birth until 12 months of age. The prevalence of Lactobacillus reuteri was higher in the faeces of infants whose mothers had taken the active supplement compared with those whose mothers had taken placebo.

The highest prevalence was recorded at 5–6 days of age (82% in treated vs. 20% in placebo; p<0.001). The first expressed breast milk (colostrum) was positive for Lactobacillus reuteri in 12% of the mothers given Lactobacillus reuteri and in 2% of mothers in the placebo group. Breast-feeding seemed to reduce faecal Lactobacillus reuteri counts while antibiotics did not appear to have any effect. Lactobacillus reuteri supplementation did not appear to affect bifidobacteria or C. difficile colonisation.

Conclusion:
Lactobacillus reuteri can be detected in breast milk after oral supplementation to the mother and in almost all infants after oral supplementation during the first year of life. Lactobacillus reuteri can also occasionally be detected in the faeces of untreated infants.