Abee and others (1994) in a study on the mode of action of nisin Z against L. monocytogenes found that the addition of nisin Z caused an immediate loss of cellular K, depolarization of the cytoplasmic membrane, hydrolysis and partial efflux of cellular ATP and an inhibition of respiration activity in L. monocytogenes. We therefore hypothesize that the use of a potassium phosphate saline instead of sodium phosphate saline might offset the loss of intercellular K+ caused by the ability of nisin to form channels in the cytoplasmic membrane and disrupt the PMF of Listeria cells.