Not so sterile: bacteria exposure begins in the womb

Western Australian researchers have used rigorous contamination controls to confirm that exposure to bacteria begins in the womb, laying to rest the longstanding question of whether or not the womb is sterile. Their work has been published in the journal Frontiers in Microbiology.

“Over the last decade, numerous studies have detected bacterial DNA in amniotic fluid and first-pass meconium [baby’s first poo], challenging the long-held assumption that the womb is sterile,” said lead author Dr Lisa Stinson, from The University of Western Australia (UWA). “However, some argue that the results are false positives — contaminants in the reagents used in DNA analysis.”

To settle the issue, Dr Stinson and colleagues collected amniotic fluid samples from 50 healthy women undergoing planned caesarean deliveries, later followed by meconium samples from their babies’ first bowel movements. The researchers took strict measures to eliminate bacterial contamination; for example, they purified the reagents used to amplify traces of bacterial DNA in the samples, by adding an enzyme which digests DNA remnants from biomanufacturing.

“Despite these measures, we still found bacterial DNA in almost all samples,” Dr Stinson said.

“Interestingly, the meconium microbiome varied hugely between individual newborns. The amniotic fluid microbiome for the most part contained typical skin bacteria, such as Propionibacterium acnes and Staphylococcus species.”

It is important to conclusively determine whether the healthy womb harbours bacteria, the researchers say, because this ‘foetal microbiome’ would likely have a significant impact on the developing immune system, gut and brain. And given that none of the women or their babies had any sign of infection, the microbiome may indeed prove to be a beneficial regulator of early development.

“We found that levels of important immune modulators in meconium and inflammatory mediators in amniotic fluid varied according to the amount and species of bacterial DNA present,” Dr Stinson said. “This suggests that the foetal microbiome has the potential to influence the developing foetal immune system.”

There is, however, one small caveat — technically, the DNA in these samples could have come from bacteria that were already dead in the womb. According to Dr Stinson, “... the next step will be to show whether these [bacteria] are alive and constitute a true microbiome”.

Image credit: ©stock.adobe.com/au/Sebastian Kaulitzki

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