Antimicrobial peptides, bacteriocins, produced by lactic acid bacteria were adsorbed on the cells of producing strains and other gram-positive bacteria. pH was a crucial factor in determining the degree of adsorption of these peptides onto cell surfaces. In general, between 93 and 100% of the bacteriocin molecules were adsorbed at pHs near 6.0, and the lowest (c5%) adsorption took place at pH 1.5 to 2.0. On the basis of this property, a novel isolation method was developed for bacteriocins from four genera of lactic acid bacteria. By using this method we made preparations of pediocin AcH, nisin, sakacin A, and leuconocin Lcml that were potent and concentrated. This method produced a higher yield than isolation procedures, which rely on precipitation of the bacteriocins from the cell-free culture liquor. It is simple and can be used to produce large quantities of bacteriocins from lactic acid bacteria to be used as food biopreservatives.
An antimicrobial peptide designated pediocin AcH was isolated from Pediococcus acidilactici strain H. The pediocin AcH was purified by ion exchange chromatography. The molecular weight of pediocin AcH was determined by SDS-PAGE to be about 2700 daltons. Pediocin AcH was sensitive to proteolytic enzymes resistant to heat and organic solvents, and active over a wide range of pH. Pediocin AcH exhibited inhibition against several food spoilage bacteria and foodborne pathogens including Staphylococcus aureus, Clostridium perfringens and Listeria monocytogenes. It was bactericidal to sensitive cells and acted very rapidly. The bactericidal effect was not produced by either cell lysis or apparent loss of membrane permeability.
The peptide, pediocin AcH, from Pediococcus acidilactici H binds to the cell surface of Lactobacillus plantarum NCDO 955, its resistant mutant and several other sensitive and resistant Gram‐positive bacteria but not to Gram‐negative bacteria. Sensitive cells, following treatment with pediocin AcH, lost intracellular K ions, u.v.‐absorbing materials, became more permeable to ONPG and, in some strains, lysed. Binding of pediocin AcH was maximum at pH 6.0. Anions of several salts inhibited binding of pediocin AcH but this was overcome by increased concentrations of pediocin AcH. Treatment of sensitive cells with 1% SDS, 4 mol/1 guanidine‐HCl, several organic solvents and enzymes did not reduce subsequent binding of pediocin AcH. Partially purified cell wall from a sensitive strain was also able to bind pediocin AcH. However, treatment of the cell walls to remove lipoteichoic acid prevented binding. These molecules might, therefore, be one of the binding sites of pediocin AcH.
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