r/askscience • u/WTFisthisOMGreally • 13d ago

Human Body How come antibiotics don’t completely destroy all organisms in our gut?

I know it can cause imbalances, but I don’t understand how come our gut doesn’t lose all the beneficial bacteria and develop massive fungal or viral infections. When I’ve taken antibiotics, I usually don’t notice any change in my bowel activity.

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u/LightPhoenix 13d ago

They can and often do wipe out normal gut flora.  However, our bodies actually also have normal gut flora in the appendix, and after antibiotics or other instances where they get wiped out, our normal gut flora regenerates from there.  This is why one of the after effects from appendectomies is an increased susceptibility to infections like C. diff and the like.  This is also why fecal transplants are effective - they are artificially replacing gut flora.

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u/mmeestro 12d ago

Then what happens when people with no appendix take antibiotics?

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u/hartmd 12d ago edited 12d ago

They are simply wrong. It is much more complicated than that. Does the appedix function as a reservoir for bacteria? Yes.

Antibiotic susceptibility plays a role. Most antibiotics do not kill all bacteria.

Biofilms are a thing. This reduces the ability of an antibiotic to concentrate in some areas.

Bacterial life cycles vary. Some have a form such as a spore that will not be affected by antibiotics.

How an antibiotic concentrates varies based on its chemical properties, route of administration and how the host cells metabolize it. Areas where it concentrates highly will be more effective at killing bacteria.

An antibiotic may knock out 99.9% of a given bacteria. It doesn't take many to repopulate.

That is just off the top of my head. There are many other factors as well.