Its not just with Bacteria, Its insects as well
People will use pesticides to kill insects, A small percentage of insects are immune to that pesticide. Since insects reproduce very qucikly fairly quickly you will have a group of insects immune to a certain pesticide and you have to switch pesticides to kill more insects as the remaining insects have selectivly become immune to the pesticide.
If you ever read about pest problems in the house, they will tell you to change brands every 3 months or so , so you wont have this problem