Which drug example is known to disrupt cell membrane function in gram-negative bacteria?

Polymyxins are a class of antibiotics that disrupt cell membrane function specifically in gram-negative bacteria. They do this primarily by binding to the negatively charged lipopolysaccharides in the outer membrane of these bacteria. This binding leads to an alteration in membrane integrity, causing increased permeability and ultimately resulting in cell death. Gram-negative bacteria have a unique cell wall structure that includes an outer membrane, making them particularly susceptible to polymyxins compared to gram-positive bacteria, which lack this outer membrane.

In contrast, the other drugs listed function through different mechanisms. Rifampin inhibits bacterial RNA synthesis, which is not related to membrane function. Streptomycin targets the bacterial ribosome, affecting protein synthesis, while sulfonamides interfere with metabolic pathways by inhibiting folic acid synthesis. Therefore, polymyxins are specifically effective at disrupting the membrane of gram-negative bacteria, making them the correct choice in this context.