From the time they are born, babies are given a "starter pack" of bacteria from their mum that is vital for their future health.
Nearly 60 per cent of a baby's microbiome in their first 30 days of life is inherited from their mum, according to a new study of 120 Dutch mothers and their babies.
This seeding of essential communities of microbes occurs in babies that are vaginally born as well as those born via a caesarean section.
The study was published today in Cell Host and Microbe.
While caesarean babies got less of their mum's gut and vaginal microbes, they received more of their microbiome through breast milk than vaginally born babies.
The study was the first to track multiple colonies of microbes in both mothers and babies, said Wouter de Steenhuijsen Piters, a physician and data scientist at the University Medical Center Utrecht in the Netherlands.
Along with the gut, which is most often studied, other parts of the body such as the skin and respiratory system are home to billions of microscopic flora.
“We wanted to have a better idea of how the infant microbiome develops in different parts of their bodies and how it's influenced by factors such as birth mode, antibiotic use, and lack of breastfeeding,” Dr de Steenhuijsen Piters said.
Building a microbiome
To trace the development of an infant's microbial community over time, the researchers took samples from the babies' skin, nose, saliva and gut two hours after they were born, and again when they were aged one day, one week, two weeks, and one month.
They also took samples from the mums' skin, breast milk, nose, throat, faecal matter and vagina.
The study found that different parts of the mother's microbial communities seeded different parts of the infant's microbiome.
While it was unclear which specific microbes were delivered via breast milk, Dr de Steenhuijsen Piters said the finding suggests there are alternative and compensatory routes to seed the microbiomes of babies that missed out on gut and vaginal flora when they were born.
"It helps to get breast milk microbes that push the gut microbiome out in the right direction," Dr de Steenhuijsen Piters said.
"But we can't say whether giving breast milk will fully compensate for the lack of gut/vaginal microbes."
Even if a mum couldn't breastfeed, which was common, essential microbes could be acquired from other sources such as from the mum's skin or respiratory tract.
"There are so many sources there, and likely there's overlap."
Three years to play with
Emad El-Omar, director of the UNSW Microbiome Research Centre, said the study offered reassurance to mums who had given birth by caesarean section.
"The most important message coming out of it would be the compensation that occurs despite of the mode of delivery," Professor El-Omar said.
"I always get asked this question, 'I've had a caesarean section. Is my baby doomed?' That's not the case at all.
"The beauty of the microbiome is you can change it.
"There's plenty of stuff you can do to protect that baby for the future."
The first three years between birth and toddlerhood are thought to be critical for the development of the microbiome and its implications for conditions ranging from asthma and allergies to diabetes and heart disease.
And while the starter kit in the first month was important, Professor El-Omar said there was still potential to build a healthy microbiome when babies go onto solids.
"We should really be paying a lot of attention to what we feed our babies and children moving forward," he said.
"You've got three years to try and get the most healthy and diverse [microbiome]."
Mums the number-one source of microbes
Lisa Stinson, a reproductive biologist and molecular microbiologist at the University of Western Australia, said while it was well-known that caesarean sections could impact the infant microbiome, the suggestion there were alternative routes of transmission was very exciting.
"Something that we're seeing coming through in different studies is that if you breastfeed your caesarean-delivered baby, you can help to rescue the microbiome to a certain extent," Dr Stinson said.
She said the study also highlighted the importance of mum as the number-one source of microbes for their baby, and the need to protect her microbiome during the critical period.
"If we give her antibiotics during that really critical period, that will have an impact on the infant microbiome," Dr Stinson said, adding that she believed giving antibiotics during delivery has more of an effect on the baby's gut flora than the method of birth itself.
Dr Stinson said antibiotics affected populations of bacteroides and bifidobacteria found in the gut and in breast milk.
"What we really need to do is follow these infants later in life to see exactly how this early microbiome perturbation affects their lifelong health," she said.
Following up unanswered questions
The Dutch study will continue to follow the mothers and babies for the next five years.
"We'll be looking at health outcomes like, for example, susceptibility to allergy in these children and lung function," Dr de Steenhuijsen Piters said.
And there are still many unanswered questions from this study about babies' microbiome.
"There's still 40 per cent that we don't know where the child gets its microbiome from," he said.
Some of these questions could also be answered by microbiome studies in Australia.
"We know that the human microbiome differs from place to place," said Dr Stinson, who is involved in the BLOSOM study following 85 mother-and-baby pairs in Western Australia over two years.
Meanwhile, the MothersBabies study headed by Professor El-Omar is tracking the health status of more than 500 women from the time they were trying to fall pregnant right through until the child reaches five years old.
It is also taking samples from the women's partners along the way.
"We have no idea what the other contributors to the baby's microbiome are in terms of siblings, fathers or partners," Professor El-Omar said.
