how can we be cured by antibiotics after the bacteria have developed resistance?

What you must first understand is that there are a number of different ways that a bacteria becomes resistant to antibiotics. There are some bacteria that are simply resistant to certain antibiotics because they lack the target of the antibiotic. For instance. Sinorhizobium meliloti is resistant to an antibiotic (the name of which escapes me) because the shape of its 16S ribosomal RNA is not compatible with it. No matter how much of that antibiotic I use I will not be able to affect this bacteria. This type of resistance is much different than the type of resistance that comes in the form of a plasmid (a reproductive vector that bacteria can exchange information with). Genetic resistances like these are the result of the bacteria actively producing -some protein- to interfere with the antibiotic or to protect itself in some way. If the bacteria is resistant in this way it can still be killed by that bacteria if it is consistently present and in high dose. A little bacteria can only devote so much energy to this protection and its own regular processes. Most nosocomial and resistant infections use the latter type of protection so it is still possible to kill them. Similarly, antibiotic resistances like these stress the bacteria, which may allow your own immunity to get a fighting chance.

I hope this has helped.

the bacteria must be tested in the lab to see what kind of antibiotics will kill it. then that drug is administered to the patient A.S.A.P,

cuz people like short term stuff
not long term progress