The mode of delivery and infant diet seem to affect the gut microbiome of six-week-old infants, according to a new study published online in the Journal of the American Medical Association (JAMA) Pediatrics. Experts found that babies who were delivered by caesarean section have different composition of bacteria than the ones who were delivered vaginally, and the same result was observed in babies who were fed breast milk and formula milk.

The researchers studied the link between delivery, feeding methods and the gut bacteria composition of 102 infants. Seventy of them were delivered vaginally and 32 were by C-section. Seventy babies were breastfed, 26 were fed a combination of breastmilk and formula, while six of them received only formula.

The team noted that the bacteria from the group Bacteroides, which is important in developing immunity, were common in babies delivered vaginally. The infants delivered by caesarean section have high levels of Staphylococcus, which is associated with disease.

Moreover, Lactococcus were also more common in babies who consumed formula alone. The experts do not know yet the extent of how this type of bacteria affects health. Study co-author Juliette Madan, a neonatologist at Children's Hospital at Dartmouth-Hitchcock in Lebanon, New Hampshire, remarked in a Huffington Post report that all infants who were fed the breast milk and formula combination shared a similar microbiome composition with infants who were exclusively fed with formula.

The researchers admit that they cannot confirm that these differences in gut bacteria composition automatically translate to different health outcomes. The team thinks that exposure to maternal vaginal microflora and breast milk expose babies to specific microbes that can influence the establishment of the core microbiome. This may be the clue to understanding the differences in immune development that impact the risk of acquiring diseases.

"Understanding the patterns of microbial colonisation of the intestinal tract of healthy infants is critical for determining the health effects of specific alterable early-life risk factors and exposures,” the researchers concluded. "To this end, we have identified measurable differences in microbial communities in the intestinal tracts of infants according to their delivery mode and diet, with possible consequences for both short- and long-term health."