When antibiotics were first invented, they were hailed as a magic bullet that would solve all disease forever. Miraculously, the same pill cured a number of diseases at the same time. Infections killed many fewer people, as the bacteria that caused the disease could not endure the chemical onslaught.
Unfortunately, the laypeople thought that antibiotics were effectively magic anti-disease pills. Even today, there are people who want antibiotics prescribed to them to cure colds, which are caused by viruses and not affected by antibiotics. Agriculture has been giving animals antibiotics for a prophylactic use, and none of this happens in a vacuum.
Bacteria existed before humans, and would easily survive almost all the events that would end humans. They reproduce every 15 minutes on average, and have a long history of chemical warfare against each other, and adaptation to survive harsher and harsher environments. It wasn't long before one bacteria genetically developed a way to survive the presence of antibiotic drugs. People using the antibiotics in strange ways gave this bacteria an advantage, since stopping and starting the treatment gave it time to recover and spread its genes to the non-resistant. (Bacteria are capable of sharing some of their genes by swapping, even without reproducing. This sharing helps them survive environments that change frequently.)
Nowadays, antibiotic resistant bacteria are quite common, and more and more antibiotics are becoming useless. There are even bacteria that require antibiotics to survive. Researchers are using this by making genetically engineered bacteria that require antibiotics. Should the bacteria become contaminated with unwanted genes, they can be killed off by ending the supply of antibiotics. It also keeps some of the wild germs out. However, this is quite bad for us, since the usual means of treating disease isn't working so great anymore, and if somebody comes to the hospital with a serious infection, they could die of it as easily as before antibiotics were invented.
This are two pieces of good news here. One is that an alternative has been developed. In the Soviet Union, antibiotics were in short supply, so doctors there developed viruses that destroyed common bacteria, and went inert when there were no more bacterial cells to infect. They call this "Bacteriophage," from "Bacteria," and "phage," Greek for "eating." Bacteria do not have any real defense against bacteriophages, which adapt and change like any other virus. The down side of that is that bacteriophages are specific to the type of bacteria, and must be specially developed. The process isn't difficult, but does involve culturing the original disease, identifying it, and injecting the patient with the correct phage. The process takes at least 2 days.
The other piece of good news is that antibiotic resistant bacteria gain their resistance at a cost, and are, in the absence of antibiotics, weaker than their non-resistant brethren. Pre-antibiotic treatments should prove extra effective, particularly eating sterile food, drinking sterile water, rest, and perhaps non-antibiotic drugs, if available. If the patient avoids antibiotic drugs, recovery is likely.
What you can do to keep antibiotics useful is to use them only when a doctor tells you to, to follow the instructions exactly, and to finish the entire prescription even if you feel better. (You feel better before all bacteria are destroyed.) This way, you will not breed antibiotic resistant bacteria. If you are a doctor, phage therapy shows significant promise.