Differences in susceptibility of Listeria monocytogenes strains to sakacin P,sakacin A,pediocin PA-1, and nisin

Two hundred strains of Listeria monocytogenes collected from food and the food industry were analyzed for susceptibility to the class IIa bacteriocins sakacin P, sakacin A, and pediocin PA-1 and the class I bacteriocin nisin. The individual 50% inhibitory concentrations (IC(50)) were determined in a microtiter assay and expressed in nanograms per milliliter. The IC(50) of sakacin P ranged from 0.01 to 0.61 ng ml(-1). The corresponding values for pediocin PA-1, sakacin A, and nisin were 0.10 to 7.34, 0.16 to 44.2, and 2.2 to 781 ng ml(-1), respectively. The use of a large number of strains and the accuracy of the IC(50) determination revealed patterns not previously described, and for the first time it was shown that the IC(50) of sakacin P divided the L. monocytogenes strains into two distinct groups. Ten strains from each group were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of whole-cell proteins and amplified fragment length polymorphism. The results from these studies essentially confirmed the grouping based on the IC(50) of sakacin P. A high correlation was found between the IC(50) of sakacin P and that of pediocin PA-1 for the 200 strains. Surprisingly, the correlation between the IC(50) of the two class IIa bacteriocins sakacin A and sakacin P was lower than the correlation between the IC(50) of sakacin A and the class I bacteriocin nisin.