I recently read Good Gems, Bad Germs as part of my effort to learn more about bacteria, viruses, how are bodies work, cells, microbiology etc.. It is a great book, I highly recommend it. Page 111:

Since bacteria can grow remarkably quickly, eliminating all but a small number just means that the new population boom will come from those few, resistant, ancestors. But that is not the only reason bacteria are so challenging to fight. They have been around billions or years and have survived because they can adapt well. Bacteria, in fact, can get their genes from distantly related bacteria. So if one bacteria gains immunity another bacteria can get that immunity by getting genes from that other bacteria (seems like science fiction but it is actually science fact).

Related: Stratification and Systemic Thinking - Blocking Bacteria From Passing Genes to Other Bacteria - Misuse of Antibiotics - Understanding the Evolution of Human Beings by Country - Hacking Your Body’s Bacteria - How Bacteria Nearly Destroyed All Life