How does the microbial environment in your gut initiate?

Question

Clearly, a zygote does not harbor any microbes. As it develops, and the alimentary canal tissue is differentiated, I logically assume that there is still no microbial activity in the fetus's gut. I'm thus also assuming that the commencement of microbial activity in the intestines occurs after birth, but when, and how? Do newborn babies just happen to ingest only certain e.g., *E.coli* strains? Is the gut a selective environment in which only certain *E.coli* strains develop? Are there any mechanisms to ensure that harmful bacteria do not initially reside in the gut? Is a newborn's digestive tract particularly unstable and ineffective until the proper microbes are established?

Answer 1

This typically occurs as the infant traverses the vaginal canal, initially exposing the infant's GI tract to vaginal flora. Then, the baby's GI tract will be colonized by environmental bacteria, commonly found on food and the rest of the objects the baby comes in contact with. This idea is crucial to remember as a physician, as baby's need Vitamin K shots immediately after birth to prevent hemorrhagic disease of the newborn. If you recall from physiology, the bacteria of the gut synthesize Vitamin K to be used by the liver to form clotting factors. Baby are born without this gastrointestinal colonization, thus predisposed and at risk to hemorrhagic insult. Also, E. coli are not the only flora within the gut. Fusobacterium and several other anaerobic organisms call our GI tract home. These organisms prevent the colonization of harmful bacteria through competition for nutrients. In the setting of antibiotic use, the normal flora may be wiped out and allow for pathogenic bacteria to colonize such as C. difficile.

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