lipid-a and octapeptin-antibiotics

Octapeptins are cyclic lipopeptides with a broader spectrum of activity against fungi and polymyxin-resistant Gram-negative and Gram-positive bacteria. In the present study, we investigated the interaction of octapeptin A3 with asymmetric outer membrane models of Gram-negative pathogen Pseudomonas aeruginosa using neutron reflectometry, together with fluorimetric and calorimetry methods. For the first time, our neutron reflectometry results reveal that the interaction of octapeptin A3 with the Gram-negative outer membrane involves an initial transient polar interaction with the phospholipid and lipid A headgroups, followed by the penetration of the entire octapeptin molecule into the fatty acyl core of the outer membrane. This mechanism contrasts with that of polymyxin B, which specifically targets lipid A, whereas octapeptins appear to target both lipid A and phospholipids. Furthermore, the mechanism of octapeptins does not appear to be highly dependent on an initial complementary electrostatic interaction with lipid A, which accounts for their ability to bind to lipid A of polymyxin-resistant Gram-negative bacteria that is modified with cationic moieties that act to electrostatically repel the cationic polymyxin molecule. The presented findings shed new light on the mechanism whereby octapeptins penetrate the outer membrane of polymyxin-resistant Gram-negative pathogens and highlight their potential as candidates for development as new antibiotics against problematic multi-drug-resistant pathogens.

Topics: 1,2-Dipalmitoylphosphatidylcholine; Carbohydrate Conformation; Cell Membrane; Drug Resistance, Multiple, Bacterial; Lipid A; Lipid Bilayers; Lipopeptides; Polymyxin B; Protein Binding; Pseudomonas aeruginosa; Unilamellar Liposomes

Polymyxin-resistant pmrA mutants of Salmonella typhimurium differed from their parents in that they were resistant to tris(hydroxymethyl)aminomethane-ethylenediaminetetraacetate-lysozyme, tris(hydroxymethyl)aminomethane-ethylenediaminetetraacetate-deoxycholate, and tris(hydroxymethyl)aminomethane-ethylenediaminetetraacetate-bacitracin. Tris(hydroxymethyl)aminomethane-ethylenediaminetetraacetate released about 50% less lipopolysaccharide from the pmrA strains than from the parental strains when the bacteria were grown in L-broth containing 2 mM Ca2+. Protamine, polylysine, octapeptin, benzalkonium chloride, cold NaCl, cold MgCl2, or cold tris(hydroxymethyl)aminomethane hydrochloride (pH 7.2) caused no leakage or markedly less leakage of periplasmic beta-lactamase from a pmrA mutant than from its parent strain. pmrA mutants were more resistant than their parent strains to protamine and polylysine but not to octapeptin or benzalkonium chloride, as measured by the ability of these agents to kill the bacteria or to sensitize them to deoxycholate-induced lysis. The pmrA strains did not differ from their parent strains in sensitivity to several antibiotics, in porin function (as measured by cephaloridine diffusion across the outer membrane), or in outer membrane-associated phospholipase A activity.

Topics: Anti-Bacterial Agents; Bacteriolysis; beta-Lactamases; Cations; Deoxycholic Acid; Drug Resistance, Microbial; Edetic Acid; Lipid A; Lipopeptides; Lipopolysaccharides; Mutation; Oligopeptides; Peptides; Peptides, Cyclic; Polylysine; Protamines; Salmonella typhimurium