Vertical supplementation with bifidobacteria via the mother’s milk is beneficial for short and long-term infant health and is both safer and more effective than direct probiotic administration, study authors confirm.
“This study demonstrated that small amounts of maternally ingested bacteria could translocate to the infant gut via oral- and entero-mammary routes in more than half of the mother infant pairs, suggesting it is feasible to nourish infants with bifidobacteria and possibly other probiotic bacteria via lactation.”
Their research findings “deepen the understanding of mother-infant bacterial transmission” and offer valuable insights into basic science and industrial probiotic product development, they say.
The composition of infant microbiome is determined by maternal taxonomy, experts believe, although the degree and timing of bacterial transfer is unclear (whether at the perinatal or postpartum stage, for example).
The consensus suggests infant gut microbiome is established pre-birth, however infant microbiota drastically evolves postpartum and takes three years to mature. Therefore, it follows that maternal diet and lactation play a key role in colony formation for some years to come.
“A large body of literature supports that mothers’ microbiota could be transmitted vertically to infants; however, direct evidence, particularly on a fine taxonomic level, is still lacking,” the authors explain.
“Thus, it would be of interest and indeed crucial to grasp the window of opportunity for programming the gut microbiota, especially through maternal diet and lactation.”
To test the theory pertaining to vertical bacteria transmission, the authors selected a biomarker strain, Bifidobacterium (B.) animalis subsp. lactis Priobio-M8, to track mother-to-infant transfer through breast milk.
Researchers recruited 11 mother-infant pairs at the lactation stage, with mothers required to ingest M8 dry powder daily (one sachet, containing 6x1010 colony-forming units M8). The dose was ten times higher than normally recommended but was crucial to enhance detection of the target strain, researchers maintain. More than 2,800 bacterial colony clones were tested to provide taxonomic identification.
The team was unable to recruit enough pairs to include a control group due to constraints imposed during the Covid-19 pandemic.
Breast milk and mother and infant faeces were collected continuously once or twice weekly for 8-15 weeks after baseline. Milk samples of 0.5 ml and faeces were diluted in phosphate buffer saline (PBS) and incubated anaerobically to target B. animalis subsp. lactis.
High-throughput screening, strain-level metagenomics, and Phenotype MicroAssay analysis were performed to detect M8 homologous isolates from the powder, as well as from breast milk and faecal samples from subjects.
Analyses revealed that a high number of M8 clones adapted to environmental conditions through genomic polymorphism, particularly in the sugar transporter glcU gene, the authors write.
“The mutation frequency of this gene was as high as 49.2% across 195 mother-infant isolates. It was detected in eight mother-infant pairs, implicating extremely strong directional selection pressure.
They speculate that cross-transmission from mother to infant, may compel M8 to expand its metabolic repertoire to increase efficiency in utilising intermediate products generated in fermentation by other bacteria as a carbon source.
“Especially, it is known that metabolic cross-feeding often occurs between bifidobacterial and gut microbiota,” they comment.
All maternal faecal samples tested positive for M8 homologous isolates, which was expected given the large M8 dose, its strong tolerance and high survival rate through the gastrointestinal tract, the authors say.
Most mother-infant pairs (54.5%) contained M8, so it was therefore “logical to postulate” that the probiotic gained access to the infant gut through breast milk.
“The high frequency of M8 homologous isolates recovered from most breast milk samples strongly supported that oral and entero-mammary routes of bacterial translocation exist and are common to most individuals,” they write.
M8 was detected in the maternal faeces and milk of four pairs (36.4%) but not in the corresponding infant faeces and could be attributed to the “scantiness” of target bacteria. Alternatively, the authors considered biological reasons that may affect host survival and/or colonisation ability of M8 homologous bacteria.
One family pair registered positive for clones in maternal and infant faeces but not breastmilk samples, while M8 was not present in five other infant faecal samples.
“The success in bacterial colonisation has been reported to be a personalised process linking to both host factors and microbiome features.
“On the other hand, it was also possible that the vertical transmission in this case was via alternative and yet to be identified path other than the proposed oral- and entero-mammary routes.”
The maintain that the risk of sample contamination was a concern and cannot be completely ruled out but assert that the study design was sufficiently robust to convincingly validate the original hypothesis.
‘Bifidobacterium animalis subsp. lactis Probio‑M8 undergoes host adaptive evolution by glcU mutation and translocates to the infant’s gut via oral‑/entero‑mammary routes through lactation’
Authors: Zhi Zhong, Hai Tang, Tingting Shen, Xinwei Ma, Feiyan Zhao, Lai‑Yu Kwok, Zhihong Sun, Menghe Bilige and Heping Zhang