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Where do bacteria in our body come from?

  1. Aug 30, 2012 #1
    We know that alot of bacteria are present in our body like in our stomach etc. Where do they come from? It's hard to think that at fertilization there is information stored somewhere in the fertilized egg that these bacteria are to be produced which will help in digestion. In other words they probably have to come through the environment. Thoughts?

    By the way if they do come through the environment, why are'nt they attacked by the immune system?
  2. jcsd
  3. Aug 30, 2012 #2


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    I believe (not sure about this) that the initial inoculation of gut bacteria comes from your mother. We were told that this is one of the advantages of breast-feeding. After a population of bacteria is introduced, of course they multiply in your gut. I think your immune system doesn't start up immediately after birth, so these beneficial bacteria can get classified by your immune system as part of "self". I'd be interested to hear other comments on whether this is correct.
  4. Aug 30, 2012 #3

    Simon Bridge

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    Is this a chicken-and-egg question?

    The symbiotic fauna/flora/things (for example) in our bodies do get attacked by our immune system - depending on what they do to trigger it. They enter our bodies in the womb or soon after we are born and during birth itself.

    These organisms have evolved with us into a symbiotic relationship over a very long time. If they were not good at getting into us, and living there, they would not be symbiotic.

    @phyzguy: babies immune systems get supercharged just after birth - it's just not all their own. Their own system has to learn to recognize new threats and respond properly but is already capable of responding to a wide range of challenges - including controlling their own gut bacteria.

    I keep reading, but having trouble confirming, that gut bacteria is often transferred from the mother's anus during a vaginal birth. It is certainly what all the newborn health books said when we had our son.

    Antibodies also cross the placenta and linger for some months after birth. They also get a regular top-up of antibodies and lymphocytes in the breast milk.
    Last edited: Aug 30, 2012
  5. Aug 30, 2012 #4

    Andy Resnick

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    My understanding is that gut flora primarily get there from eating. And yes, those bacteria have to survive the passage. Lactobacillus acidophilus is a common dietary supplement, for example.
  6. Aug 30, 2012 #5
  7. Aug 30, 2012 #6
    Yes, this is what advertisers of probiotic yoghurt like to call ‘friendly’ bacteria. But that isn’t quite the correct understanding. As Simon Bridge said, the correct term is ‘symbiotic’ relationship, which basically just means mutually beneficial. The enzymes the bacteria produce to allow them to access certain nutrients in the food we eat, also help us to access nutrients as well. But it wasn’t ever thus. There were some generations of what Sean Carroll calls an ‘evolutionary arms race’ that took place between our ancestors and those of the bacteria before it settled down into a symbiotic relationship. And that doesn’t mean the bacteria can’t harm us. The same enzymes they produce that help us when produced in our bowel make us very sick if produced in our stomach. The bacteria do not have a direct route from the bowel to the stomach. Enough said about their usual route to get there if I say, make sure you wash your hands properly after using the toilet!
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