64.下列何種抗生素具有陽離子界面活性劑的作用？
(A)bacitracin
(B)polymyxins
(C)rifampin
(D)tylosin

polymyxin B 和 E 都是只對抗陰性菌

Polymyxin E (Colistin)

• prevention and treatment of Enterobacteriaceae infections
• 經濟動物生長促進劑
• 口服不吸收>>所以專幹腸道感染 (沙氏桿菌，大腸桿菌引起之下痢)
• The bacterial cell membrane is the initial site of action for colistin.
• Colistin binds to LPSs and phospholipids in the outer cell membrane of Gram-negative bacteria.
• It competitively displaces divalent cations (Ca2+ and Mg2+) from the phosphate groups of membrane lipids, which leads to disruption of the outer cell membrane, leakage of intracellular contents and bacterial death against many Gram-negative bacteria