Polymyxins are a class of antibiotics that are primarily used to treat serious bacterial infections, especially those caused by gram-negative bacteria. There are several synonyms for the word "polymyxins", including colistin, polymyxin E, and polymyxin B. These antibiotics are derived from the bacteria Bacillus polymyxa and are effective against several types of bacteria, including those that are resistant to other types of antibiotics. Polymyxins work by binding to the bacterial cell wall and disrupting the cell membrane, causing the bacteria to die. While they are powerful antibiotics, polymyxins can have serious side effects and are generally reserved for use in severe infections where other treatments have failed.