Agents that increase the permeability of the outer membrane (OM) of Gram-negative bacteria include cationic agents, chelators, and other compounds that interact with the OM's lipopolysaccharide (LPS). The OM is a barrier that prevents the passage of hydrophobic molecules and large hydrophilic compounds, but cationic agents such as polymyxins, polymyxin nonapeptides, and lysine polymers can disrupt this barrier by binding to LPS and altering its structure. These agents can increase the permeability of the OM, allowing hydrophobic compounds and antibiotics to enter the cell. Other cationic peptides, such as defensins, cecropins, magainins, and melittin, also have OM-permeabilizing effects, though their mechanisms of action may differ. Chelators such as EDTA can also increase OM permeability by removing divalent cations that stabilize the LPS structure. The molecular mechanisms of OM permeability increase involve the disruption of LPS-LPS interactions and the formation of phospholipid bilayer patches in the OM. Some bacterial strains, such as pmrA mutants of Salmonella typhimurium, are resistant to OM-permeabilizing agents due to altered LPS structures. These strains have reduced binding of cationic agents and are less sensitive to OM-permeabilizing effects. Buffer ions such as Mg²⁺, Ca²⁺, and Na⁺ can compete with cationic agents for binding sites on LPS, reducing their OM-permeabilizing effects. The OM-permeabilizing action of cationic agents is often reversed by physiological concentrations of NaCl and divalent cations. The effectiveness of these agents can vary depending on the bacterial strain and the specific conditions of the experiment. In summary, cationic agents and chelators can increase the permeability of the OM by disrupting LPS structure and altering the physical properties of the OM. These agents are useful tools in studying the OM's role in bacterial resistance and in developing new antimicrobial strategies. However, their use is limited by the potential toxicity and the resistance of certain bacterial strains to these agents.Agents that increase the permeability of the outer membrane (OM) of Gram-negative bacteria include cationic agents, chelators, and other compounds that interact with the OM's lipopolysaccharide (LPS). The OM is a barrier that prevents the passage of hydrophobic molecules and large hydrophilic compounds, but cationic agents such as polymyxins, polymyxin nonapeptides, and lysine polymers can disrupt this barrier by binding to LPS and altering its structure. These agents can increase the permeability of the OM, allowing hydrophobic compounds and antibiotics to enter the cell. Other cationic peptides, such as defensins, cecropins, magainins, and melittin, also have OM-permeabilizing effects, though their mechanisms of action may differ. Chelators such as EDTA can also increase OM permeability by removing divalent cations that stabilize the LPS structure. The molecular mechanisms of OM permeability increase involve the disruption of LPS-LPS interactions and the formation of phospholipid bilayer patches in the OM. Some bacterial strains, such as pmrA mutants of Salmonella typhimurium, are resistant to OM-permeabilizing agents due to altered LPS structures. These strains have reduced binding of cationic agents and are less sensitive to OM-permeabilizing effects. Buffer ions such as Mg²⁺, Ca²⁺, and Na⁺ can compete with cationic agents for binding sites on LPS, reducing their OM-permeabilizing effects. The OM-permeabilizing action of cationic agents is often reversed by physiological concentrations of NaCl and divalent cations. The effectiveness of these agents can vary depending on the bacterial strain and the specific conditions of the experiment. In summary, cationic agents and chelators can increase the permeability of the OM by disrupting LPS structure and altering the physical properties of the OM. These agents are useful tools in studying the OM's role in bacterial resistance and in developing new antimicrobial strategies. However, their use is limited by the potential toxicity and the resistance of certain bacterial strains to these agents.