Birthwrite

The infant microbiome

Kate Nash and Debra Sloam consider preventive and restorative strategies required to support the infant microbiome, and the midwife’s role in relation to this

The human microbiome is the collective term for all the microorganisms and their genetic material, known as microbes, that live and thrive upon and within our bodies.This includes bacteria, viruses, fungi, archaea and protozoa.Trillions of microbes are encompassed within the human microbiome, and these can be separated into subsections dependent on their location within the body. For example,‘gut microbiomes’ refers to the microorganisms (and their genes) that reside in our gastrointestinal system (The Human Microbiome Project Consortium, 2012; Prescott, 2017). The terms microbiota and microbiome are often used synonymously. However, there is a difference, as the microbiome definition refers to microorganisms and their genetic material, whereas the microbiota refers only to the microbes themselves.The microbiome is not exclusive to the human race, as animals, plants, soils and oceans all have their own microbiomes.

The human microbiome is an essential part of biology that supports many physiological functions and plays a major role in maintaining human health.The vertical transmission of microbiota from mothers to their infants has occurred throughout a period of millions of years, representing hundreds of thousands of host generations and untold billions of bacterial generations.The microbiome is a symbiotic ecosystem that has evolved alongside humanity and connects us to our ancestors and genetic lineage (Moeller et al, 2014).

Kate Nash Senior lecturer, University of the West of England Debra Sloam Lecturer, University of West London

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The infant microbiome begins to develop in utero and is exposed to maternal microbes during birth, affecting its structure.

The development of the infant microbiome commences in utero. During pregnancy, maternal microbiota may indirectly affect the fetus through the maternal immune response, microbial factors that may cross the placenta or through factors such as stress or diet (RomanoKeeler and Weitkamp, 2015;Weaver et al, 2017). Both the maternal gut and vaginal microbiota change with gestational age, and it is thought this may enhance metabolic and epithelial function. Lactobacilli bacteria dominate the mother’s vagina in preparation for birth and breastfeeding (DominguezBello et al, 2019).

The fetus gains exposure to maternal vaginal and perineal microbes following rupture of the chorioamniotic membranes, as maternal microorganisms are soaked into the infant’s skin and sensory organs and are swallowed (Dominguez-Bello et al, 2010; 2019). During vaginal birth, an infant is likely to have contact with maternal fecal matter, and this exposure to maternal gut microbes facilitates infant gut colonisation.The structure of the infant microbiome is affected by this maternal transfer of microbiota, which help develop the newborn’s immature gut and immune system (Mueller et al, 2015).These influence diverse physiological processes, including energy metabolism, obesity, glucose homeostasis, blood pressure control and behaviour (Dominguez-Bello et al, 2016).

The extent to which childbirth practices may interfere with maternal transmission of microbiota are not completely understood, although evidence suggests that operative birth and exposure to intrapartum antibiotics alter bacterial colonisation and the construction of the infant microbiome (Stearns et al, 2017).While caesarean birth can be a life-saving procedure, the infant is unlikely to have acquired the full set of its mother’s vaginal microbes, because they do not pass completely through the birth canal. Prophylactic antibiotics administered to prevent infection associated with major abdominal surgery are also likely to alter the mother’s microbiome and in turn, the infant’s microbiome. An infant born by elective caesarean section is also likely not to have been exposed to the stresses, pressures and hormone releases associated td

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British Journal of Midwifery, May 2022, Vol 30, No 5