Antibiotic resistance is a serious medical problem. Genes that confer resistance to antibiotics can be readily transferred from one bacterial species to another, and the cells that acquire these traits are better able to evade the effects of the drugs we rely on to treat these infections. One way to test bacteria for drug resistance is to spread a culture of the cells onto a growth medium in a Petri dish. The bacteria multiply and spread, forming a "lawn." Onto this lawn are placed small discs that contain a specific antibiotic. If the cells are sensitive to an antibiotic, a clear "halo" will form around the disc—an area in which no bacteria have grown.
The figure shows two Petri dishes, each containing bacteria isolated from a different patient. The discs contain three different antibiotics. Based on these data, which conclusion is correct?