microbial colonization...,

thescientist |  Infants start out mostly microbe-free but quickly acquire gut bacteria, which take root in three successive groups. First, Bacilli dominate. Then Gammaproteobacteria surge, followed by Clostridia. But the pace at which these bacterial groups colonize the gastrointestinal tract depends on the time since the babies were conceived, not since when they were born. And time since conception appears to have more of an influence on the infant gut microbiome than other factors, such as exposure to antibiotics, whether babies were born vaginally or by cesarean section, and if they were breastfed. These are a few of the findings from a survey of 922 fecal samples collected from 58 premature babies, published today (August 11) in PNAS.

“It is an interesting study that provides useful data regarding temporal changes in microbial composition in the infant gut that can be mined further,” Shyamal Peddada, a biostatistician at the National Institute of Environmental Health Sciences who was not involved in the study, wrote in an e-mail to The Scientist.

“I think the paper does a nice job of showing that premature babies develop differently from full-term babies . . . it is not just a function of colonization after birth,” Rob Knight from the University of Colorado, Boulder, told The Scientist in an e-mail. “Differences in gut physiology or in the infant immune system could explain this pattern.”

Researchers at the Washington University School of Medicine in St. Louis embarked on this survey in an effort to better understand the role of the microbiota in the development of gut disorders common in premature infants, such as necrotizing enterocolitis. Without first defining the premature infant gut in the absence of gastrointestinal issues, the researchers struggled to identify potentially pathogenic bacterial patterns.

The researchers collected stool samples each time the babies defecated until they were thirty days old, and sampled every third elimination after that. They then sequenced 16S ribosomal RNA genes to identify the bacterial composition of each sample.