Strategy for manipulation of cheese flora using combinations of lacticin 3147-producing and -resistant cultures

The aim of the present study was to develop adjunct strains which can grow in the presence of bacteriocin produced by lacticin 3147-producing starters in fermented products such as cheese. A Lactobacillus paracasei subsp, par acasei strain (DPC5336) was isolated from a well-flavored, commercial chedd ar cheese and exposed to increasing concentrations (up to 4,100 arbitrary u nits [AU]/ml) of lantibiotic lacticin 3147, This approach generated a stabl e, more-resistant variant of the isolate (DPC5337), which was 32 times less sensitive to lacticin 3147 than DPC5336, The performance of DPC5336 was co mpared to that of DPC5337 as adjunct cultures in two separate trials using either Lactococcus lactis DPC3147 (a natural producer) or L, lactis DPC4275 (a lacticin 3147-producing transconjugant) as the starter. These lacticin 3147-producing starters were previously shown to control adventitious nonst arter lactic acid bacteria in cheddar cheese. Lacticin 3147 was produced an d remained stable during ripening, with levels of either 1,280 or 640 AU/g detected after 6 months of ripening. The more-resistant adjunct culture sur vived and grew in the presence of the bacteriocin in each trial, reaching l evels of 10(7) CFU/g during ripening, in contrast to the sensitive strain, which was present at levels 100-to 1,000-fold lower, Furthermore, randomly amplified polymorphic DNA-PCR was employed to demonstrate that the resistan t adjunct strain comprised the dominant microflora in the test cheeses duri ng ripening.