Microbiology: Breastfeeding affects viral colonization of the infant gut

Colonization of the infant gut by viruses after birth may be modulated by breastfeeding reports a paper published in Nature this week. The study suggests that viral colonization occurs in stages and that partial or exclusive breastfeeding may protect infants against some human viruses.

At birth, the gut of the infant is devoid of viruses. However, it quickly becomes colonized with microorganisms, including viruses, although the process of the assembly of the viral population is not well understood.

In order to investigate early-life viral colonization, Frederic Bushman and colleagues analysed stool samples from 20 healthy infants 0–4 days after birth and then again at 1 and 4 months of age. In the first four days after birth virus-like particles could not be detected; however, one month later particles were detected in most samples. To determine the origin of the viral populations, the authors performed genome sequencing and found that shortly after birth, pioneer bacteria colonize the infant gut and by one month of age, bacteriophages (bacteria-infecting viruses) are the main source of the virome community. By four months of age, identifiable viruses that replicate in human cells (such as adenoviruses and picornaviruses) have become more prominent.

The authors then compared their virus data to variables such as, feeding history, mode of delivery and sex. They discovered that breastfeeding was associated with a lower accumulation of viruses that replicate in human cells. To validate their findings, the authors obtained stool samples from a separate cohort of 125 infants taken at 3–4 months of age. In this cohort, the authors identified human viruses in stool samples of 30% of the formula-fed babies. In comparison, human viruses were identified in stool samples of 9% of babies fed with breast milk or with both breast milk and formula.