Hiroshi Nikaido

Characterized the outer membrane of gram-negative bacteria as a barrier to antibiotics and toxic agents. Proved the lipid bilayer of this membrane was asymmetric, which retarded passage of lipophilic solutes including many antibiotics. Discovered porin channels that allow small nutrient molecules to cross the outer membrane rapidly.

Discovered and characterized multidrug efflux pumps of unusually broad specificity as another important factor to prevent the entry of drugs into the cytoplasm of gram-negative bacteria.