A food-grade system for production of pediocin PA-1 in nisin-producing and non-nisin-producing Lactococcus lactis strains: application to inhibit Listeria growth in a cheese model system.

Food-grade heterologous production of pediocin PA-1 in nisin-producing and non-nisin-producing Lactococcus lactis strains, previously selected because of their technological properties for cheese making, was achieved. Plasmid pGA1, which contains the complete pediocin operon under the control of the strong P32 promoter and is devoid of any antibiotic marker, was introduced into L. lactis ESI 153 and L. lactis ESI 515 (Nis+). Transformation of L. lactis ESI 515 with pGA1 did not affect its ability to produce nisin. The antimicrobial activity of the pediocin-producing transformants on the survival of Listeria innocua SA1 during cheese ripening was also investigated. Cheeses were manufactured from milk inoculated with 1% of the lactic culture and with or without approximately 4 log CFU/ml of the Listeria strain. L. lactis ESI 153, L. lactis ESI 515, and their transformants (L. lactis GA1 and GA2, respectively) were used as starter cultures. At the end of the ripening period, counts of L. innocua in cheeses made with the bacteriocin-producing lactococcal strains were below 50 CFU/g in the L. lactis GA1 cheeses and below 25 CFU/g in the L. lactis GA2 ones, compared with 3.7 million CFU/g for the controls without nisin or pediocin production.