Using a diagram of a Gram-negative envelope (outer membrane, periplasmic space with peptidoglycan, inner membrane), indicate the sequence of events after a polymyxin molecule binds the bacterial surface. Which sequence is correct?

• A. Electrostatic binding to LPS → insertion of hydrophobic tail into outer membrane → disruption/permeabilization of outer membrane → penetration to inner membrane and permeabilization → ion leakage and cell death.
• B. Passive diffusion through porins into cytoplasm → inhibition of DNA replication enzymes → accumulation of unrepaired DNA breaks → secondary outer membrane disruption.
• C. Binding to peptidoglycan crosslinks → prevention of cell wall synthesis → immediate outer membrane collapse due to loss of structural crosslinks between membranes and wall.
• D. Enzymatic cleavage of lipids in the periplasm → generation of toxic intermediates that diffuse outward and selectively degrade the outer membrane without affecting the inner membrane.

Answer: (A)