Research provides clues as to how gut microbiota affect infant health

BMJ 2013; 346 doi: (Published 14 February 2013) Cite this as: BMJ 2013;346:f1017
  1. Bob Roehr
  1. 1Washington, DC

Two studies provide new information on how gut microbiota may contribute to the overall health of infants and why a melamine contaminant in pet food, milk, and formula has proved so deadly to some.

A study in the journal of the Canadian Medical Association found significant differences in the commensal bacterial population of healthy infants at four months, depending on whether they were delivered naturally or by caesarean section and whether they were breast or bottle fed.1

The small but intensely studied sequential sample of 24 healthy term infants for whom a stool sample was available was conducted as part of the Canadian Healthy Infant Longitudinal Development (CHILD) study, which plans to take samples from more than 2000 infants several times over the course of their development.

There were equal numbers of boys and girls. A quarter (six) of the infants were delivered by caesarean section. Ten were exclusively breast fed; five were partly breast fed, with supplementation by bottle; and nine were exclusively fed by bottle.

Bacterial richness and diversity were lowest among infants born by elective caesarean delivery and highest among those born by emergency caesarean delivery. Exposure at delivery through the birth canal is thought to be the primary way an infant acquires gut microbiota. Caesarean delivery exposes the infant to a different microbial population, while an emergency delivery is likely to expose the child to microbiota from both locations in the mother’s body.

Breast feeding exposes the infant to additional populations of the mother’s skin microbiota and to components of her immune defenses present in breast milk, which can affect initial colonization by microbiota of the child’s gut.

“The potential long-term consequences of decisions regarding mode of delivery and infant diet are not to be underestimated,” the authors wrote. “Infants born by caesarean section are at increased risk of asthma, obesity, and type 1 diabetes, whereas breastfeeding is variably protective against these and other disorders.”

The second study, in Science Translational Medicine, pointed to gut microbiota as the crucial variable that turned melamine into a deadly renal toxin.2

The genesis of the study was the 2008 incident in China when the industrial chemical melamine was illegally added to pet food, milk, and infant formula because it seems to boost protein count when products are analyzed.3 The compound previously had been thought to be acutely toxic only at very high doses.

But in a series of experiments in animal models the researchers identified Klebsiella terrigena as the essential component. The bacterium is a common part of human and animal gut microbiota at a variety of concentrations. The researchers believe that it turns melamine into cyanuric acid, which can quickly crystallize with melamine and uric acid in renal tubules.

The most common occurrence is the formation of kidney stones, but in this instance of poisoning the process was more widespread and the damage to kidneys greater. The lead author, Xiaojiao Zheng, and colleagues theorized that the animals and infants that died had a higher concentration of Klebsiella terrigena in their gut microbiota at the time of their exposure to melamine.

The findings offer evidence that differences in gut flora composition among individuals can lead to different—and sometimes poisonous—reactions to the same drugs, foods, and environmental chemicals.


Cite this as: BMJ 2013;346:f1017