The cause of antibiotic resistant forms is the use of antibiotics themselves. These resistant forms are found in what are considered "native" or "natural" communities. Each of the members is slightly different, just as you and I am.
Changing the environment by adding an antibiotic, we are selecting for ones who have the genes that allow them to thrive.
Not all antibiotic use does this. Some communities do not have the genes to resist.
Staph aureus has those with resistant genes and so does tubercle bacillus.
To control these bacteria we have to find other antibiotics. We can cause multiple antibiotic forms to arise by doing that.
Progress is happening to see if there are solutions to this problem.
MERSA has been transferred and covers this plate. A disc of Oxacillin has been placed in the center and the plate has been incubated for a day. If the Oxacillin would control this streak, there would be a ring of clear agar around the disc.