Bifidobacterium longum subsp. infantis M-63 Can Reach the Neonatal Gut Following World Health...

The World Health Organization (WHO) recommends reconstituting powdered infant formula with water at ≥70°C to reduce risk of bacterial contamination. Although this practice is important for microbiological safety, it may also reduce the viability and/or functional activity of heat-sensitive bioactive components, such as probiotics. However, it remains unclear whether probiotics added to infant formula can reach the infant gut under WHO-recommended preparation conditions.

To evaluate whether Bifidobacterium longum subsp. infantis M-63 (B. infantis M-63) added to infant formula can be detected in the neonatal gut when the formula is prepared with water at ≥70°C, following WHO recommendations.

In this exploratory, randomized study with 2 supplementation levels, 34 term neonates received formula containing B. infantis M-63 reconstituted according to WHO-recommended conditions, from birth to 1 mo of age. Fecal recovery of the administered strain was assessed, together with analyses of gut microbiota composition and fecal metabolite profiles. Concurrent breastfeeding was permitted without restriction to reflect real-world feeding practices.

Although reconstitution at ≥70°C substantially reduced viable bacterial counts in the prepared formula, B. infantis M-63 was detected in fecal samples at high rates at 1 mo of age (low-dose 94.4%, high-dose 100%), with no significant differences in detection rates or fecal counts between dose groups. Gut microbiota composition shifted toward a Bifidobacterium-dominant profile over time regardless of dose. In addition, fecal recovery of the administered strain was positively associated with specific tryptophan-derived metabolites, including indole-3-lactic acid (ρ = 0.509, P = 0.002).

Under WHO-recommended infant formula preparation conditions, B. infantis M-63 was detected in nearly all infants, together with a gut microbiota profile characteristic of early infancy. These findings provide in vivo evidence that B. infantis M-63 can reach the neonatal gut and suggest potential biological activity under microbiologically safe and practically relevant preparation conditions. This trial was registered at clinicaltrials.gov as UMIN000058303.