So, what you are saying is that bacteria is getting stronger because of the misuse of the drug dosage. And this bacteria when it attacks humans causes havoc, Is that the gist of it.
Yes.
Antibiotics kill/prevent growth of bacteria, which are tiny single celled organisms which live in colonies with millions of them. Their numbers can grow very rapidly if the colony has good conditions (Like in our bodies).
Some of them can cause diseases if we get infected with them so we take antibiotics to kill them off and prevent further growth if our own immune system cannot handle them.
Problem is that not all bacteria in a colony are genetically exactly the same, just as not all humans of a certain population are genetically the same.
For example, a patient got infected with some sort of bacteria and had to take antibiotics to kill them in his body.
But some of those millions of bacteria might be a little bit more resilient against the antibiotic because of different genes and dont die as fast as most of the other bacteria.
So after most of the bacteria have been killed, the patient feels better and stops taking the antibiotics (Which is exactly what you should not do), but those which are a little bit stronger due to their genes are still in the body.
So those surviving bacteria (with the better genes) get the chance to replicate and pass on their genes onto the next generation. And then this new generation passes their genes (Including those which make them more resilient) onto the next generation and so on.
And over a certain amount of time, they get completely resistant against antibiotics.
Its simply what Darwin described in his theory of evolution... just much much much faster (Unfortunately).