Use of bacteriocinogenic lactic acid bacteria to inhibit spontaneous nisin-resistant mutants of Listeria monocytogenes Scott A.

Nisin is a bacteriocin with a broad antibacterial spectrum including strains of Listeria monocytogenes. Populations of L. monocytogenes, however, frequently contain spontaneous nisin-resistant mutants. When a culture of L. monocytogenes Scott A was exposed to nisin concentrations between 10 and 500 IU ml-1, the initial decrease in viable numbers was followed by regrowth of survivors to nisin. Nisin-resistant mutants of L. monocytogenes Scott A were isolated after a single exposure to nisin at 100 IU ml-1 and were shown to be sensitive to the non-nisin bacteriocins, sakacin A and enterocin B, produced by Lactobacillus sake Lb 706 and Enterococcus faecium BFE 900, respectively. The regrowth of L. monocytogenes Scott A following the initial decrease due to exposure to nisin was prevented by nisin-resistant Lact. sake Lb 706-la and to a somewhat lesser extent, by Ent. faecium BFE 900-6a. Listerial cells surviving nisin action were thus inhibited by the bacteriocin-producing strains that might be used as starter or protective cultures in foods. Growth of a nisin-resistant mutant of L. monocytogenes Scott A (Li3) was also suppressed by the bacteriocinogenic cultures. Use of nisin in combination with a starter culture producing a non-nisin antilisterial bacteriocin may therefore prevent the emergence of nisin-resistant mutants of L. monocytogenes.