Neomycin, an aminoglyoside with antimicrobial spectrum similar to gentamicin, binds to the 30S subunits of the bacterial ribosome, inhibiting protein synthesis and thereby disrupting DNA synthesis. It is active against many gram negative aerobes and against some strains of staphylococci.
Bacitracin inhibits bacterial cell wall synthesis and is active against many gram-positive bacteria (e.g. staphylococci, streptococci, corynebacteria and Clostridia) and some gram-negative species (e.g. Neisseria and Haemophilus influenzae). They are often found in combinations in topical preparations as broad spectrum antibacterial agents.
Polymyxin B disrupts the bacterial cytoplasmic membrane of mostly gram positive organisms allowing leakage of intracellular constituents by binding to membrane phospholipids.