Antibiotics come in all types, but the first, and still most important type, is called beta-lactam. Beta-lactam is a very small, very special ring, that, when it binds to the wall of most bacteria it breaks the wall and pops the bacteria. But there are so many bacteria, that eventually, one of them discovers a way to stop the beta-lactam ring. That means that the antibiotics don’t work! Even worse, they won’t work on the children of that bacteria, meaning you get rapid growth again. How do they do it? They produce a protein that can accept the beta-lactam ring, without harming the cell wall.
Antibiotics can still defeat these bacteria, but it requires more and more beta-lactam. You can try this out yourself by starting the simulation by pressing the button. Then quickly clicking in this simulation to make more beta-lactam. If you wait too long you may never be able to get to the cell membrane (the wall that protects the cell). Keep in mind, it takes more than one shot to get rid of the membrane.