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 s trains of Lister-in monocytogenes. Populations of L, monocytogenes, ho wever, frequently contain spontaneous nisin-resistant mutants. When a culture of L. monocytogenes Scott A was exposed to nisin concentration s between 10 and 500 IU ml(-1), the initial decrease in viable numbers was follow-ed by regrowth of survivors to nisin. Nisin-resistant muta nts oft. monocytogenes Scott A were isolated after a single exposure t o nisin at 100 IU ml(-1) and were shown to be sensitive to the non-nis in bacteriocins, sakacin A and enterocin B, produced by Lactobacillus sake Lb 706 and Enterococcus faecium BFE 900, respectively. The regrow th of L. monocytogenes Scott A following the initial decrease due to e xposure to nisin was prevented by nisin-resistant Lact. sake Lb 706-1a and to a somewhat lesser extent, by Ent. faecium BFE 900-6a. Listeria l 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 Scot t A (Li3) was also suppressed by the bacteriocinogenic cultures. Use o f nisin in combination with a starter culture producing a non-nisin an tilisterial bacteriocin may therefore prevent the emergence of nisin-r esistant mutants of L. monocytogenes.