Babies' Guts Host Bacteria, Viruses

Viruses are present in the guts of newborn babies, according to findings published in Nature Medicine.

Researchers from Washington University School of Medicine in St. Louis studied eight newborns — four sets of healthy twins – from birth until two years old to chart the gut viral microbiome (the “virome”) and bacterial microbiome in a longitudinal analysis.

Many aspects of this field of research have long been centered on the gut bacterial microbiome, which is rapidly acquired after birth, but not much had been known about the virome. The researchers suspected that the development of both was essential to immune development and influential on health in adulthood.

“We are just beginning to understand the interplay between all the different types of life within our gut,” senior author Lori R. Holtz, MD, assistant professor of pediatrics, explained in a press release. “They are not stand-alone communities. We also are seeing that the environment of the infant gut is extremely dynamic, which differs from the relative stability that has been shown in adults.”

The researchers took stool samples from the newborns between their first and fourth days of life, and saw that viruses were present even then. Some of the viruses the researchers identified were known to infect cells of the human hosts, but others infected the gut bacteria.

“We were surprised that right from the beginning quite a diversity of viruses was found in the gut,” Holtz continued. “It prompts the question ‘where do these viruses come from?’ We don’t know yet whether diet, method of the baby’s delivery, or other environmental influences play a role.”

The researchers say they may attribute the population in the bacterial microbiome and the virome to a “predator/ prey relationship,” meaning the viruses that kill bacteria end up without prey. The virome population declines, and afterward, the bacteria microbiome cells are able to flourish.

“The predator/ prey dynamic is still a hypothesis at this point,” Holtz said. “It probably has been best described in bacteriophage and bacteria living in oceans. But this relationship could explain the populations of viruses and bacteria we see, how they change over time, and how they may stabilize as we age.”

Anelloviruses were also present in the infants’ samples. As anelloviruses reflect humans’ immune statuses, more viruses present means the immune system is weakened.

“One child had at least 47 anellovirus strains at the 12-month sampling,” Holtz said, and added that nearly all of the anelloviruses discovered were previously unidentified. “It’s important to remember that these are healthy children living in the community. We wondered if we would see a wide diversity of anelloviruses at this age because the children are losing the mother’s immune protection that they have had since birth, and they are still in the process of building up their own immunity in this interval.”