Interactive Features | Health

Explore the Human Microbiome [Interactive]

Learn about the bacteria, fungi and other micro-organisms that maintain human health.



The body contains 10 times more bacteria, fungi and other micro-organisms than human cells. Most of these species are harmless—although they can still cause illness if they wind up in the wrong place. In addition, researchers are beginning to learn exactly how some microbial species in the body help digestion and contribute to regulation of appetite and the immune system.  

Illustration by Bryan Christie

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  1. 1. ENVME 06:38 PM 5/15/12

    This is an interesting and probably unanswerable question. If all cells weighed the same, the bacteria, fungi and other microbes in a 160 lb. (~73 kg) human, assuming a 10 to 1 ratio in favor of the non-human organisms, would weigh 144 lb. (~65 kg). This seems to me unlikely. Additionally if mitochondria is factored in, which likely is an ancient intruder, an uninfected human would weigh something like the approximate amount of a newborn baby. I am looking forward to comments on this by others having more knowledge than my simple calculations.

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  2. 2. TheHigginbotham1024 in reply to ENVME 10:18 PM 5/15/12

    It is unlikely because in your described calculations you assume that all cells weigh the same. In reality, prokaryotic cells (bacteria) are far smaller than eukaryotic cells (human cells). prokaryotic cells are usually 1-10 micrometers across, whereas eukaryotic cells are usually 10-100 micrometers across. Furthermore, there is a fair amount of weight that is not comprised of cells, extracellular matrix such as that in cartilage and in bone. Even when factoring in mitochondria, the vast majority of the mass of a human is strictly human, that is to say the product of our DNA.

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  3. 3. jwkerby2 in reply to ENVME 10:56 PM 5/15/12

    Prokaryotic cells are about an order of magnitude smaller than eukaryotic ones. Also, we have a lot of non-cellular material that makes up our body that doesn't count towards the number of "us" cells.

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  4. 4. jwkerby2 in reply to ljnester 10:58 PM 5/15/12

    Actually very little. All of your body, minus your GI tract, mouth, skin, and nasal passages, is generally sterile. That's not to say that this isn't impressive, just misleading.

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  5. 5. jimcummins 12:08 AM 5/16/12

    I'm not sure that mitochondria should be counted here, as they are such ancient (and essential) commensals they should be regarded as "us". I've seen estimates of several Kg of microbia in the gut making up the bulk of feces.

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  6. 6. Mike Winkelman 10:51 AM 5/21/12

    Fascinating article. Mindful of the possible role of H. Pylori in controlling obesity, and the fact that this commensal bacteria is now absent in the microbiome of so many younger people, are you aware of any efforts to introduce it? Could this become a new Probiotic?

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  7. 7. Vivekbabu 11:12 AM 5/21/12

    Here 1:10 is just about the cell count not about the mass of the cells...

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  8. 8. PatrikD 05:54 PM 5/21/12

    In the last episode of his excellent "Meet the Scientist" podcast, Carl Zimmer talks with Martin Blaser about H. pylori and the possible reasons and consequences of its disappearance in the human microbiome. Highly recommended - check it out: http://blogs.discovermagazine.com/loom/2010/12/30/losing-our-germs-my-last-podcast/

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  9. 9. egrivel 06:56 PM 5/27/12

    Just read the article in the paper edition, really fascinating. What I'm wondering is -- how do all these different types of bacteria get into the body in the first place? Especially those that are at home in the gut? Wouldn't they die when exposed to a "normal" environment?

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  10. 10. brenniewinters 02:58 PM 6/18/12

    There are good and bad bacteria and viruses. Proper hand washing with soap and water kills most. Dishes and laundry need to be cleaned with hot soapy water and rinsed well. The dryer kills most harmful ones.
    Blood and body fluids are always to be considered contaminated.
    When I was a Nurse in California, one doctor said place a small amount of triple antibiotic ointment in your nose before you go into public to stop mersa.
    Kissing and sex spread many germs and viruses.
    Clothing carries many of these from person to person.

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  11. 11. brenniewinters in reply to jwkerby2 03:00 PM 6/18/12

    As a retired Nurse I know this is not true. Many people carry diseases many years with no symptoms.

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  12. 12. S_Babylon in reply to ENVME 06:05 PM 6/18/12

    I'd question the inclusion of mitochondria as well. We are driven by our metabolic processes to feed our hungry brains. The mitchondria lines we have are absolutely integral to the development of a human.

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  13. 13. tigerwoof in reply to brenniewinters 12:03 AM 10/14/12

    Sounds frightening...Glad i dont think those thoughts.

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