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Bacteria in the human body: when we die and when we are born

  1. Jun 11, 2015 #1
    It is said that around 90% of the cells in a human body are symbiotic bacteria living thanks to us.
    When we die, do most of them also die? Or do they manage to survive without us and find a new 'home human'?

    And opposite, when and how do we get all those bacteria after conception? Do we get some already from the mother while embryos in the womb? If so when do they start to 'invade' our body? Or do we get them only after birth and by which mechanisms?
  2. jcsd
  3. Jun 11, 2015 #2
    I doubt it's as much as 90% of the human body mass, though micro organisms do exist in large quantities in the digestive tract and help in breaking down food into substances that can be easily absorbed.
    I guess the original population probably does come from the mother, but after birth more will be added later when consuming food.
    Most of the food we eat and water we drink is far from being sterile and only a few microbiota found in food are potentially hazardous.
  4. Jun 11, 2015 #3


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    The 90% figure refers to the fraction of cells in your body that are bacterial, not the mass.
  5. Jun 12, 2015 #4
    Indeed, thanks
  6. Jun 12, 2015 #5
    It is an interesting question. Presumably if bacteria and other components of the biome could evolve a way to get into a new animal at death than it would be very much to their advantage.

    My suspicion is that one way is they might transform into some kind of dormant mode capable of surviving in soil until ingested by another animal... a bit like the way prion diseases propagate.
    Alternatively, they might hope to survive in water courses.

    If they need to harden themselves for the transition then do they have some kind of quorum sensing mechanism to detect when death occurs? Perhaps even cause death?
    Maybe something to consider when reading about the 'death wave':

    But there are known ways that they are transmitted - I understand a main one is during birth - one of the unknowns about birth by caesarean section is how much of a disadvantage it is not to get so much of the mother's biome.
  7. Jun 12, 2015 #6

    Andy Resnick

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    Our gut becomes colonized by bacteria by eating- newborns do not have gut bacteria, this is one of the reasons why their diet is so different (early immunity comes from mother's milk). There is a discussion about the differences in gut bacteria between 'natural' and delivery by Ceasarean, but I don't know the current state of knowledge. I don't know how long it takes for bacteria to colonize, but it's reasonably short- weeks. Also, for many animals, an early meal is fecal matter- that is a very efficient way to get bacteria into the gut.
  8. Jun 12, 2015 #7


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