Antimicrobial membrane

Plantaricin A (PInA), KSSAYSLQMG AT AIKQVKKL FKKWGW, an antimicrobial 26-peptide pheromone produced by Lactobacillus plantarum Cll. The cationic PltiA has antimicrobial membrane-permeabUizing activity, and is exported out of the ceU by a bacteriocin-secretion machinery. It acts as a pheromone by interacting with membrane-associated histidine protein kinase of a three-component... 

The mechanism of action of quats has been widely studied. It is generally agreed that their iateraction with the bacterial cell membrane is the primary event resulting ia antimicrobial activity (16,17). 

In subsequent studies attempting to find a correlation of physicochemical properties and antimicrobial activity, other parameters have been employed, such as Hammett O values, electronic distribution calculated by molecular orbital methods, spectral characteristics, and hydrophobicity constants. No new insight on the role of physiochemical properties of the sulfonamides has resulted. Acid dissociation appears to play a predominant role, since it affects aqueous solubiUty, partition coefficient and transport across membranes, protein binding, tubular secretion, and reabsorption in the kidneys. An exhaustive discussion of these studies has been provided (10). 

Nonoxidizing Antimicrobials. Nonoxidizing antimicrobials usually control growths by one of two mechanisms. In one, microbes are inhibited or killed as a result of damage to the ceU membrane. In the other, microbial death results from damage to the biochemical machinery involved in energy production or energy utilization. 

Considerable work has been done to try to explain why quats are antimicrobial. The following sequence of steps is beheved to occur in the attack by the quat on the microbial cell (/) adsorption of the compound on the bacterial cell surface (2) diffusion through the cell wall (J) binding to the cytoplasmic membrane (4) dismption of the cytoplasmic membrane (5) release of cations and other cytoplasmic cell constituents (6) precipitation of cell contents and death of the cell. 

The intended application of an antimicrobial agent, whether for preservation, antisepsis or disinfection, will influence its selection and also affect its performance. For example, in medicinal preparations the ingredients in the formulation may antagonize preservative activity. The risk to the patient will depend on whether the antimicrobial is in close contact with a break in the skin or mucous membranes or is introduced into a sterile area of the body. 

The antimicrobial activity of iodine is less dependent than chlorine on temperature and pH, though alkaline pH should be avoided. Iodine is also less susceptible to inactivation by organic matter. Disadvantages in the use of iodine in skin antisepsis are staining of skin and fabrics coupled with possible sensitizing of skin and mucous membranes. 

Different organic acids, primarily lactic acid, have been successfully used for decontamination of whole livestock carcasses, and the application of different organic acids used for decontamination has also been tested in the fruit and vegetable industry. Organic acids other than lactic acid that are known to have bactericidal effects are acetic, benzoic, citric, malic, propanoic, sorbic, succinic and tartaric acids (Betts and Everis 2005). The antimicrobial action is due to a reduction in the pH in the bacterial environment, disruption of membrane transport, anion accumulation or a reduction in the internal pH in the cell (Busta et al., 2001). Many fruits contain naturally occurring organic acids. Nevertheless, some strains, for example E. coli 0157, are adapted to an acidic environment. Its survival, in combination with its low infective dose, makes it a health hazard for humans. 

Shai Y (1999) Mechanism of the binding, insertion and destabilization of phospholipid bilayer membranes by a-helical antimicrobial and cell non-selective membrane-lytic peptides. Biochim Biophys Acta 1462 55-70... 

Keywords Solid-state NMR structure analysis 19F-labeling Membrane-active peptides Native biomembranes Oriented membrane models Antimicrobial peptides... 

Unlike other Eukarya, animal cells lack cell walls, though they tend to be surrounded by a highly developed glycocalyx of up to 140 nm in thickness [108]. This diffuse layer of densely packed oligosaccharides has a heterogeneous composition and is connected to the membrane via lipids or integral proteins. The boundary of the cell usually extends beyond the mere lipid bilayer with its embedded proteins, and the extracellular structures provide initial sites of interaction or are themselves targets for MAPs such as antimicrobial peptides [115]. 

In summary, we may thus conclude that PGLa and GS do not form stable, NMR-observable pores in native membrane as readily as they do in model bilayers. The corresponding tilted and/or inserted states of our two representative MAPs could only be comprehensively characterized in DMPC-based samples, where the peptides could be trapped in a uniform state. In living cells, on the other hand, these states would seem to be only of a transient nature, i.e. at the very moment when the antimicrobial peptide attacks the membrane and passes through the lipid barrier along its concentration gradient towards the cytosol. 

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