Colistin is a last-resort drug. It is used only when all other drugs fail. These bacteria have developed resistance to colistin. Scientists fear that the bacteria could one day mutate, and it would be almost impossible to treat with current medications. However, this is not the case right now because the bacteria in question do not have a resistance to other antibiotics. Scientists recommend using antibiotics only when it is absolutely necessary to help ensure that drug-resistant bacteria do not grow and multiply rapidly.
This is straight from the course.