Such bacteria are usually sensitive only to polymyxins and tigecycline. Resistance to polymyxins first appear in 2011. Consequently, treatment methods often fall back on polymyxins, particularly colistin. Polymyxins B1 and B2 are considered major components. These include quinolones (such as fluoroquinolones), 3rd and 4th generation cephalosporins, and polymyxins, including colistin. Polymyxin B is composed of polymyxins B1, B1-I, B2, B3, and B6.