The effects on vegetative cells and spores of three bacteriocins from lactic acid bacteria

The sensitivities of vegetative cells of strains of Listeria, Clostridium, Staphylococcus, Lactococcus, Lactobacillus, Micrococcus and Pediococcus, and of spores of Clostridium and Bacillus to three broad spectrum bacteriocins (nisin A, nisin Z and pediocin) from lactic acid bacteria were determined by a critical dilution micro-assay. The minimal inhibitory concentrations (MIC) of partially purified bacteriocins, prepared by a pH-dependent adsorption/desorption process, were determined and expressed in arbitrary units ml(-1) and in mu g ml(-1) of pure bacteriocin, The MICs of bacteriocins varied considerably between species and even between strains of the same species, as clearly shown for nine strains of Listeria monocytogenes. When bacteriocin activity was expressed in mu g ml(-1), pediocin was more effective against Listeria monocytogenes than nisin A or nisin Z. The latter bacteriocins, in concentrations between 23 and 69 mu g ml(-1), prevented outgrowth of Clostridium and Bacillus spores for at least 10 days. Although pediocin at 17 mu g ml(-1) prevented outgrowth of B. stearothermophilus and C, butyricum spores for up to 7 days, it apparently activated the germination of B, subtilis spores. (C) 1999 Academic Press.