From my basic understanding, antibiotics kill living things, bacteria for example.

Do the antibiotics consumed by a human-being distinguish between what they kill? Or do they just kill every bacteria they find? And if that's the case, which bacteria do antibiotics find or do they find all bacteria in a human's body? Again, if that is the case, does that mean that after taking antibiotics for a certain time that the human body is free of all bacteria?

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    $\begingroup$ Depends on the antibiotic and whatever's in the subject's microflora. Not even "broad-spectrum" antibiotics can kill all species of bacteria. Even in "sensitive" species, there may be a few strains that have adapted a way to resist the onslaught of an administered antibiotic. Additionally, spores of some bacteria are not exactly the kind that can be killed with antibiotics... $\endgroup$
    – user132
    Commented Jan 17, 2012 at 11:02

2 Answers 2



There are several reasons why this might not be true, as Alexander has discussed. An antibiotic often has a molecular target that isn't present in all bacteria, it's extremely hard to get antibiotics to certain parts of your body, and some bacteria will be defended against a antibiotic attack by biofilms, resistance mechanisms, and sheer statistical probability.

That is not to say that many don't die. Indeed, one of the major causes of Clostridium difficile infection is that antibiotics kill most of your gut bacteria, allowing the somewhat better protected C. diff to proliferate, start producing toxins, and send you to the hospital with symptoms ranging from diarrhea to perforated colon and worse. That disease is a direct consequence of "Antibiotics kill some but not all bacteria in you".

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    $\begingroup$ The species epiphet is difficile. :) As I alluded to in the comments, spores aren't the sort of things that are affected by antibiotics. Even if you manage to kill off vegetatives, the spores will remain, and can start turning to vegetatives again once the antibiotics wear off. $\endgroup$
    – user132
    Commented Jan 17, 2012 at 12:32
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    $\begingroup$ Bloody autocorrect on the new OS grumble $\endgroup$
    – Fomite
    Commented Jan 18, 2012 at 0:49

Just a quick answer: No, there is no way to kill all bacteria in your body once they are there. The only way to keep a person sterile is to prevent any bacteria entering the guts during and all time after the birth. Look for gnotobiology and gnotobionts to learn more about these organisms (including humans).

Here are some reasons why:

  1. Most antibiotics have selective action on certain type of bacteria. This is due to the mechanisms involved in their action, permeability through the bacterial wall, their effective concentrations etc. Even broad-spectrum antibiotics have selective action. None is universal (and it is hardly possible to create those).

  2. Antibiotics can't reach all the places in your body. Many bacteria either create some barrier against the immune response or the body eventually builds one. In the worst cases the whole bacterial infection is isolated and petrified (calcifications), as it is the case for tuberculosis and so-called Gohn's complex in lungs.

  3. As long as you are not isolated from the society and secluded into a sterile box you will have a steady contact with millions of bacteria which re-invade your skin and guts. There is no way you can stop it and your gut flora will beging to restore spontaneously.

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    $\begingroup$ "Many bacteria ... create some barrier against the immune response..." - indeed, colonies of bacteria can form biofilms that are impervious to antibiotics. $\endgroup$
    – user132
    Commented Jan 17, 2012 at 11:53
  • $\begingroup$ A follow up point: bacteria actually seems to transfer from mother to baby in the womb, so even birth by cesarian in a sterile environment wouldn't produce sterile babies. Which is a good thing, since they'd probably die without a healthy established colony. ncbi.nlm.nih.gov/pubmed/18281199 $\endgroup$ Commented May 23, 2013 at 19:26
  • $\begingroup$ I'd also like to add that gnotobionts are not per se germ-free. Gnotobiontic (from the greek gignoskein, γιγνώσκω, to know) animals have a known flora. Although one could also argue that germ-free animals also have a know flora, namely none. $\endgroup$
    – Wolgast
    Commented Mar 29, 2015 at 16:28

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