“The problem is that the types of bacteria that could potentially harm a newborn infant like these neutral pH aerobic conditions,” says Leach. “Bifidobacterium help by rapidly using up the oxygen and creating an anaerobic environment which drops the pH. This limits the growth of potentially harmful bacteria.”
However, scientists are only just at the beginning of understanding how all this fits together. “It may be more nuanced than ‘caesarean section is less good and vaginal delivery is better’,” says Field. “Not all vaginal-born babies got the bugs which were associated with reduced risk, and not all caesarean section babies got the health outcomes that we were worried about.”
Microbe engineering
Nevertheless, the finding raises the question – should we intervene to give babies (and especially babies born via C-section) a helpful microbial boost? “C-sections save lives and so our job is to rebuild the missing microbiome, safely and precisely,” argues Mishra.
The question is how. One option sometimes considered is “vaginal seeding”, whereby a swab of vaginal fluid is smeared on a newborn’s skin and mouth in the hope that beneficial microbes will take root in the baby’s gut.
The practice is growing in popularity, yet experts warn it could transfer dangerous infectious pathogens: over a quarter of women are thought to carry group-B strep in their vagina, for example, which could be fatal to an infant. What’s more, the 2019 baby biome study showed that the beneficial microbes weren’t coming from the mum’s vagina anyway.
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There are other potential microbiome engineering options too, such as faecal microbial transplants, also called a stool or poo transplant. Here, stool from the mother could be transferred to the infant’s gastrointestinal tract. There have been some promising small scale trials, but the practice is not currently recommended.
“At the moment, we don’t know whether a mum’s vaginal or even faecal microbiome is the right one to give to a baby, and I think there’s a risk that it might not do good, and that it could do harm that we don’t yet understand,” says Field.
Probiotic supplements have been shown to be a safe and effective way to influence gut flora, however. Some clinical trials suggest that they could protect extremely premature or low birthweight infants from necrotising enterocolitis, a life-threatening intestinal disease that primarily affects premature babies, while other studies indicate they could reduce the risk of preterm birth. However, there is still the question of knowing which bacteria to provide.
“Any changes in establishing a microbiome in an infant should focus on restoring or rectifying the impact that human intervention has had on this process,” says Leach. “Vaginal seeding and faecal microbial transplants are essentially just dirty probiotics. You just don’t know what’s in them, and they carry risk. So probiotics are probably the way to go.”
Mishra also says oral probiotics may be the most practical and safest approach, although notes that results vary widely as each baby’s gut is unique.
The future, she adds, likely lies in precision microbiome interventions, guided by a baby’s genetic, dietary and immune profile. “Think of it as ‘personalised microbial medicine’,” she says.
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