>suddenly trillions of sewer bacteria get exposed to a low dose and suddenly start developing resistance.
I think you're misunderstanding how resistances work.
Bacteria don't "start developing" resistance, if they survive the antibiotic at all they already had resistance by stroke of luck. The surviving, resistant bacteria will subsequently survive and outnumber the dead, not-resistant bacteria and we generally call this "developing resistance", but the resistance itself is down to a simple question of whether it was already there or not.
Resistances do not come to existence after bacteria come across an antibiotic. If resistance is there, the dosage won't matter because the resistant bacteria will survive regardless.
> If resistance is there, the dosage won't matter because the resistant bacteria will survive regardless.
That’s not how evolution works. A few bacteria could be resistant to low doses. After the low dose, and a short wait, now the entire population is resistant to the low dose.
That gives them a much better starting point for mutations to the resistance gene and for crossing with bacteria that have some other complimentary resistance gene.
Sounds like you actually have no idea how resistance occurs. There are mechanisms for bacteria to gain resistance they didn't start out with, it's called horizontal gene transfer. At least read the wiki before you speaking so confidently about something you know so little about.
We don't really care which of those trillions of sewer bacteria carries the pre-existing genes that resist an anti-biotic; we care when a new strain starts becoming prevalent and decreasing the effectiveness. From our perspective, it's a new resistant strain.
I think you're misunderstanding how resistances work.
Bacteria don't "start developing" resistance, if they survive the antibiotic at all they already had resistance by stroke of luck. The surviving, resistant bacteria will subsequently survive and outnumber the dead, not-resistant bacteria and we generally call this "developing resistance", but the resistance itself is down to a simple question of whether it was already there or not.
Resistances do not come to existence after bacteria come across an antibiotic. If resistance is there, the dosage won't matter because the resistant bacteria will survive regardless.