[M95D]

I don't have a source or example and I don't have the time to properly search, but I can provide a quick explanation:

The vast majority of resistance mechanisms are detrimental to the cell that has them.

  1. The bacteria consumes energy to be resistant by pumping out the antibiotic, blocking it with a protein or breaking it down with an enzyme.
  2. Alters it's billion-years-optimized metabolism or structure to be resistant and this affects it's efficiency.
  3. Forgoes on a source of energy because it can't use it anymore.

You can read about these mechanisms here: https://en.wikipedia.org/wiki/Antimicrobial_resistance#Mecha...

When in a competition with regular bacteria (no antibiotic around), these resistant cells will be outcompeted and gradually replaced.