Summary: The action of bactericidal polycationic peptides was compared in spp. by testing peptide binding to live cells and changes in outer membrane (OM) morphology and permeability. Moreover, polycation interaction with LPS was studied by measuring the dependence of dansylcadaverine displacement and zeta potential on polycation concentration. When grown at 37 °C, and bound less polymyxin B (PMB) than pathogenic or non-pathogenic regardless of virulence plasmid expression. OMs were unharmed by PMB concentrations causing extensive OM blebbing in The permeability to Iysozyme caused by PMB was greater in in or and differences increased at 37 °C. Similar observations were made with other polycations using a polymyxin/novobiocin permeability assay. With LPS of cells grown at 26 °C, polycation binding was highest for and lowest for , with yielding intermediate results which were lower for pathogenic than for non-pathogenic strains. With LPS of cells grown at 37 °C, polycation binding remained unchanged for and pathogenic increased for non-pathogenic and decreased for to Y. levels. Polycation binding related in part to differences in charge density (zeta potential) of LPS aggregates, suggesting similar effects at bacterial surfaces. It is suggested that species and temperature differences in polycation resistance relate to infection route, invasiveness and intracellular multiplication of spp.


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