Mode of delivery and intestinal virome of the newborn seem to be linked
According to a new study, the mode of delivery could influence the composition of the viral flora in the intestines of newborns. Viruses themselves could play a major but still unknown role in the proper development of the intestinal microbiota.
Having a rich and diversified microbiota from the first year of life seems to ensure a lower risk of developing obesity, diabetes or intestinal disorders later in life, and the mode of delivery has a major impact on the development of this budding flora. However, studies on this subject are mainly focused on bacterial species and neglect other residents which are just as important: viruses. An Irish team partly filled this gap by carrying out the first study regarding the impact of the mode of delivery on the composition of infant virome.
More Anelloviridae in vaginal deliveries
Researchers took stool samples from 20 newborns aged one year, half of whom were born through cesarean section and the other half vaginally. Caudovirales, Microviridae and Anelloviridae were the most abundant viruses detected in both groups. However, the virome of babies born vaginally was more diverse and more abundant than that of babies born through a cesarean section. In particular, viruses from the Anelloviridae family were significantly more abundant, including the Torque Teno Virus (TTV), a virus largely spread in human population and found in all biological compartments although its role remains unknown. Previous works have shown that levels of Anelloviridae in the intestines reached a peak between the ages of 6 months and 1 year, before decreasing from the age of 15 months. Their origin is still difficult to determine because potential colonization sources are very diverse. The authors list maternal transmission during birth or breastfeeding, as well as contact with the other parent, other children or the environment as possible causes.
Predatory viruses to diversify flora?
What role do these viruses play within the intestinal microbiota? Some viruses–bacteriophages–are able to infect bacteria, including those found in the digestive flora, such as the crAssphage (cross-assembly* phage). This phage is known as a large predator of bacteria from the Bacteroidetes phylum which are present in high levels in the first months of life. Moreover, close sequences of phages infecting two different strains of Bifidobacterium longum were detected in larger numbers in newborns born vaginally. According to the authors, these results suggest that intestinal viruses play an integral part: their ability to predate on bacteria could contribute to increase the diversity of bacterial species from a very early age.
*Cross-Assembly was the technique used to detect it
A McCann et al. Viromes of one year old infants reveal the impact of birth mode on microbiome diversity. PeerJ. May 2018 7;6:e4694