The lab takes a bit of your sputum and they "grow it" on an agar plate which takes a day or so.They can then determine what bacteria you have. After it "grows" the bacteria out, they take a bit of that and place it on another agar plate and put these eraser size discs (10-15) of different antibiotics. If your bacteria does not grow around that disc then the bacteria is sensitive to that antibiotic (it should kill it), if the bacteria does grow around the disc then the bacteria is resistant to the antibiotic (will do nothing). The test is called a culture with a S & R (sensitivity & resistance).