Quantification and efficiency of Lactobacillus sakei strain mixtures used as protective cultures in ground beef

Lactobacillus sakei is a lactic acid bacterium, naturally associated with long term storage of fresh meat at low temperature. Here we investigated the effect, on the evolution of pathogenic and spoilage microorganisms in ground beef, of L. sakei cocktails used as bioprotective cultures. We selectively developed a real time quantitative PCR method, allowing the quantification of individual L. sakei strains inoculated in ground meat with specific probes. Six cocktails of three strains were tested to evaluate their effect on the growth of Salmonella enterica Typhimurium, Escherichia coli O157:H7 and Brochothrix thermosphacta at 4°C and 8°C, under vacuum or modified atmosphere packaging. Using plating methods to quantify the different bacterial species, one cocktail showed an effect against S. Typhimurium and E. coli under given conditions. Real time quantitative PCR showed that the three inoculated L. sakei strains had a different growth pattern, and that the association of these three strains indeed impaired growth of S. Typhimurium and E. coli.