Use of a genetically enhanced, pediocin-producing starter culture, Lactococcus lactis subsp. lactis MM217, to control Listeria monocytogenes in cheddar cheese

Cheddar cheese was prepared with Lactococcus lactis subsp, lactis MM217, a starter culture which contains pMC117 coding for pediocin PA-1, About 75 liters of pasteurized milk (containing ca, 3.6% fat) was inoculated with strain MM217 (ca, 10(6) CFU per ml) and a mixture of three Listeria monocytogenes strains (ca, 10(3) CFU per ml), The viability of the pathogen and the activity of pediocin in the cheese were monitored at appropriate intervals throughout the manufacturing process and during ripening at 8 degrees C for 6 months, In control cheese made with the isogenic, non-pediocin-producing starter culture L, lactis subsp, lactis MM210, the counts of the pathogen increased to about 10(7) CFU per g after 2 weeks of ripening and then gradually decreased to about 103 CFU per g after 6 months, In the experimental cheese made with strain MM217, the counts oft, monocytogenes decreased to 10(2) CFU per g within 1 week of ripening and then decreased to about 10 CFU per g within 3 months. The average titer of pediocin in the experimental cheese decreased from approximately 64,000 arbitrary units (AU) per g after 1 dag to 2,000 AU per g after 6 months. No pediocin activity (