Baby's First Bacteria (repost)

This post initially appeared on Science Blogs

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As I've noted before, our bodies are riddled with microbes - there are more of them than there are of us (if you go by shear number). But where do they come from? Each individual has a complex ecosystem of commensal (harmless) microbes that live on our skin, in our nose, mouth, ears and gut, and we lay the foundations for this ecosystem at birth. According to a new study in the Proceedings of the National Accademy of Sciences (PNAS), different methods of birth (traditional vs cesarean section) have very different outcomes in terms of what bacteria end up colonizing you:

The goal of the present study was to obtain a community-wide perspective on the influence of delivery mode and body habitat on the neonate's first microbiota[...] We found that in direct contrast to the highly differentiated communities of their mothers, neonates harbored bacterial communities that were undifferentiated across multiple body habitats, regardless of delivery mode. Our results also show that vaginally delivered infants acquired bacterial communities resembling their own mother's vaginal microbiota, dominated by Lactobacillus, Prevotella, or Sneathia, and C-section infants harbored bacterial communities similar to those found on the skin surface, dominated by Staphylococcus, Corynebacterium, and Propionibacterium.

It's been known for a long time that c-section babies were more prone to allergies and asthma, and there's a strong link between commensals and the immune system, but exactly what the difference was remained obscure. Basically, what this paper shows is that the types of bacteria that get us started are established very early.

Babies born through the traditional route are very quickly exposed to the bacterial communities of their mothers - both vaginal and gut bacteria (women often defecate when giving birth). Once these bacteria get established, they fill up all the niches, and prevent other bacteria from getting a foothold. By contrast, c-section babies don't have this initial exposure - the womb is fairly sterile, and the conditions of this surgery prevent contact with the mother's other mucosal surfaces. Because of this, the infant is ripe for colonization from the myriad of bacteria found everywhere else, from the nurses and doctors that handle them to the bacteria on the skin on the mother's breast when feeding.

It's important to note that we can't yet draw a distinct causative link between early establishment of bacterial communities and future disease (allergies, asthma etc), right now it's just correlation. And though infants are colonized by very few types of microbes, as they develop, the microbial ecosystem diversifies into thousands or millions of different species. Researchers are hard at work using new technologies to try to figure out all the different things living in an adult gut (given the spiffy name, "the microbiome"), and we've barely scratched the surface.

The one thing that is clear is that the little things living in us and on us can have a profound effect on our health, and with new research, hopefully we can use that knowledge to our advantage.