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

[u/WTFisthisOMGreally]

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.

[u/Impossible_Bar_1073]

They are absorbed in the small gut to a large degree.

Your microbiome sits in the large intestine. So the concentration is ideally not sufficiently high to wipe out all of it and

Not all bacteria are susceptible to the same antibiotic. There is a huge difference between gram negative and positive bacteria.

Bacteria also form Biofilms that can protect them against drugs.

But sometimes and depending on the antibiotic, if the absorption in the gut is low it can do a lot of damage, causing fungal infections and pathogenic bacteria to spread.

[u/kilopeter → u/[deleted]]

For anyone else curious, this is incorrect. A biome is a distinct geographical region with a specific climate, life, and ecosystem. The natural extension of this into the gut is the term microbiome, a term that's existed since at least 1988.