This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cell Wall Synthesis Inhibitors, Subject name: Pharmacology
[{'content': 'Colistin is not active against? \nSelect and explain. \nA. Pseudomonas aeruginosa, B. Serratia, C. Klebsiella pneumoniae, D. Burkholderia', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Colistin* It was obtained from B. colistinus .* It is active against gram-negative bacteria only; all except Proteus, Serratia and Neisseria are inhibited. * It is more potent on Pseudomonas, Salmonella and Shigella. Mechanism of action Rapidly acting bactericidal agent having a detergent-like action on the cell membrane. They have high affinity for phospholipids. It causes membrane distoion or pseudopore formation. It may also inactivate the bacterial endotoxin.', 'role': 'assistant'}]