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 (</p

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 (</p

From DNA sequence to application: possibilities and complications

The development of sophisticated genetic tools during the past 15 years have facilitated a tremendous increase of fundamental and application-oriented knowledge of lactic acid bacteria (LAB) and their bacteriophages. This knowledge relates both to the assignments of open reading frames (ORF’s) and the function of non-coding DNA sequences. Comparison of the complete nucleotide sequences of several LAB bacteriophages has revealed that their chromosomes have a fixed, modular structure, each module having a set of genes involved in a specific phase of the bacteriophage life cycle. LAB bacteriophage genes and DNA sequences have been used for the construction of temperature-inducible gene expression systems, gene-integration systems, and bacteriophage defence systems. The function of several LAB open reading frames and transcriptional units have been identified and characterized in detail. Many of these could find practical applications, such as induced lysis of LAB to enhance cheese ripening and re-routing of carbon fluxes for the production of a specific amino acid enantiomer. More knowledge has also become available concerning the function and structure of non-coding DNA positioned at or in the vicinity of promoters. In several cases the mRNA produced from this DNA contains a transcriptional terminator-antiterminator pair, in which the antiterminator can be stabilized either by uncharged tRNA or by interaction with a regulatory protein, thus preventing formation of the terminator so that mRNA elongation can proceed. Evidence has accumulated showing that also in LAB carbon catabolite repression in LAB is mediated by specific DNA elements in the vicinity of promoters governing the transcription of catabolic operons. Although some biological barriers have yet to be solved, the vast body of scientific information presently available allows the construction of tailor-made genetically modified LAB. Today, it appears that societal constraints rather than biological hurdles impede the use of genetically modified LAB.