My guess: before the antibiotic, the minority resistant bacteria have to compete with the majority non-resistant. After, they can proliferate freely. Repeat with the next antibiotic, and soon all the ones we see are resistant to all the antibiotics we have.
You pretty much nailed it in a very succinct manner.
That's why it's so important to complete a course of antibiotics rather than stopping once you feel better. Once you've started antibiotics, you're basically enriching the population in bacteria that aren't affected by the antibiotic. This is normally a very small population, but if you stop half-way, the pressure on those bacteria from other bacteria (the ones that died) is lower, allowing the resistant population to flourish.
If you finish a course of antibiotics, you not only kill the susceptible bacteria, but you also give your own immune system a chance to take down the few remaining bacteria that are resistant.
This is an unconvincing argument to me - if antibiotic resistant bacteria survive, why would finishing the course of antibiotics make a difference?
Does it clinically happen that stopping a course of antibiotics early causes an antibiotic resistant form of the infection?
(I couldn't find evidence either way, but I did find a few articles saying typically prescribed course lengths could be safely reduced in the effort to reduce antibiotic use generally)
>> if antibiotic resistant bacteria survive, why would finishing the course of antibiotics make a difference?
I can only speculate, but here's how I imagine it.
Your body can kill a certain number of bacteria on its own. Antibiotics help reduce the infection to the point where your body can do the rest.
If the resistant bacteria are a small minority, taking antibiotics long enough to kill most of the non-resistant ones will let your body kill the remaining resistant ones.
If you stop too early, the battle tide has not yet turned. Instead, by killing, say, half the non-resistant ones, you've made the resistant ones a larger proportion of the whole infection. Then both groups continue to multiply.
If you repeat this several times, starting and stopping the antibiotics depending on how you feel, the resistant bacteria could go from being 1% of your infection to 50%.
I can't share because that's exactly my point - as far as I can find, there isn't a single clinical example of stopping antibiotics early causing any problem of antibiotic resistance.
