Polycations as outer membrane-disorganizing agents

Abstract

The outer membrane-disorganizing effect of a short (10-ain) treatment with polycationic agents was studied with smooth Salmonella typhimurium used as a test organism. The polycationic agents were the protamine salmine, a lysine polymer with 20 lysine residues (lysine2g), and the deacylated polymyxin B derivative polymyxin B nonapeptide. Two different types of outer membranedis&$anizing action were foupd. Protamine and lysine20 released 20 to 30%o of the lipopohlys&charide from the outer membrane and sensitized the bacteria to the anioniq detergent sodium dodecyl sulfate but did not (under these conditions) make the bacteria permeable to the hydrophobic probes fusidic acid and actinomycin'D. In contrast, polymyxin B nonapeptide did not release lipopolysaccharide'or 'sensitize the bacteria to sodium dodecyl sulfate but made the outer membrane permeable to the hydrophobic probes. None of the agents was bactericidal under the conditions used or caused any leakage of periplasmic ,Blactamase. Polymyxin B was used as a reference and showe4 characteristic outer membrane-disorganizing action. In thin-section electron microscopy, polymyxin B nQnapeptide caused the appearance of long, narrow, finger-like projections on the outer membrane. Protamine and lysine20 caused a distinctly wrinkled appearance of the outer membrane but no projections.In the accompanying paper (30), we showed that growth in the presence of subinhibitory concentrations of a number of polycationic agents sensitizes smooth enteric bacteria to the hydrophobic antibiotics to which these bacteria are very resistant by nature. The active polycationic agents included protamine, a lysine polymer with 20 residues (lysine2O), and a polymyxin derivative, polymyxin B nonapeptide (PMBN), which lacks the fatty acid tail and also the antibacterial activity of polymyxin. The mechanism by which the polycations sensitize the bacteria to antibiotics was not studied. However, the polycations were shown to make the bacteria as sensitive as are the deep rough (Re) mutants that have a very defective lipopolysaccharide (LPS) in their outer membrane (OM) and, as a consequence, a profoundly disorganized OM (18). Therefore, the polycationic agents could disorganize the OM, as do also polymyxin (26) and EDTA (7).In the present paper, we characterize the action of the polycations on various parameters of OM disorganization. It should be emphasized that this paper deals with the effect of short treatment with polycations, in contrast to the long, continuous treatment described in the accompanying paper (30). We demonstrate herein a number of qualitative differences between the action of protamine and lysine20 on the one hand and PMBN and polymyxin on the other. MATERIALS AND METHODSBacterial strains. The test organism used was smooth Salmonella typhimurium SL6% (metA22 trpB2 H-i-b H2-e,n,xflaA66 rpsLI20) (34) also used in the accompanying paper. Strain SH7794 is strain SL696 carrying R plasmid R471a coding for TEM-type p-lactamase, transferred from SH9178 (29)

In Vitro Antimicrobial and Antioxidant Activity of Chitosan Isolated from Podophthalmus Vigil

“…The antibacterial mechanisms of Chitosan suggested being, the positive charge of the amino group at C-2 resulted in a polycationic structure which can be expected to interact with the predominantly anionic components (lipopolysaccharides, proteins) of the microorganisms surface (Helander et al 2002). The interaction resulted in great alteration of the structure of outer membrane (Helander et al 1998), which caused release of major proportion of proteinaceous material from the cells (Vaara and Vaara 1983). As a result, the chitosan was easier to interact with anionic components of cell surface, and exhibited higher inhibitory activities.…”

Lipopeptides as anti-infectives: a practical perspective

“…In particular, removal of the fatty acid chain by proteolytic cleavage with ficin or related enzymes resulted in deacylated nonapeptides [65], with less acute toxicity than their parent polymyxins along with a reduced antibacterial activity [66][67][68]. Despite lacking bactericidal activity themselves, these polymyxin nonapeptides (PMBN) can damage the outermost cell wall structure of Gram-negative bacteria, greatly increasing its permeability to hydrophobic antibiotics, which may facilitate combinatorial use with other antibiotics to treat specific infections [69][70][71][72][73][74][75].…”

Giardicidal activity of lactoferrin and N-terminal peptides

“…Ca 2ϩ and Mg 2ϩ block the activity of native LF, as well as other well-characterized polycationic membrane-active agents, including defensins (1,12,14,21,23). In contrast, killing by LFpep was not inhibited by any metal ion tested, except for Fe 3ϩ .…”