Final answer:
Polymyxin B is an antibiotic that damages the plasma membrane by targeting the lipopolysaccharide in gram-negative bacteria, leading to cell lysis. Its non-selective action can also harm human cell membranes, which limits its use to topical treatments or specific medical scenarios.
Step-by-step explanation:
Polymyxin B is a type of antibiotic that can cause injury to the cell's plasma membrane. This occurs because it has a specific affinity for the lipopolysaccharide components present on the surface of gram-negative bacteria. Once Polymyxin B binds to these components, it inserts itself into the membrane and disrupts the integrity of both the outer and cytoplasmic (inner) membranes. This disruption results in the leakage of cellular contents and ultimately leads to cell death or lysis.
The action of Polymyxin B resembles that of detergent, given its lipophilic (fat-loving) properties. Its mode of action is not entirely selective, which poses a risk when used systemically, as it can also affect the membranes of human cells, such as those in the kidneys and nervous system. This toxicity limits its use to topical applications or for specific, controlled circumstances. In clinical settings, due to the potency and risks associated with Polymyxin B, it is often reserved for treating infections that are resistant to other antibiotics.