GROWTH AND SURVIVAL OF LISTERIA-MONOCYTOGENES IN VACUUM-PACKAGED GROUND-BEEF INOCULATED WITH LACTOBACILLUS-ALIMENTARIUS FLORACARN L-2

A culture of the psychrotrophic strain FloraCarn L-2 of Lactobacillus alimentarius was added to ground beef (pH 5.4) inoculated with two iso lates of Listeria monocytogenes able to grow in refrigerated ground be ef. The ground beef was vacuum-packaged and stored for 9 weeks at 4 de grees C. Populations of inoculated L. monocytogenes initially were 6.3 to 6.4 log(10) CFU/g and increased to 7.4 log(10) CFU/g in ground bee f with no added lactobacilli. Addition of L. alimentarius L-2 or its a ntibiotic-resistant mutant SRL-2 reduced the final populations of L. m onocytogenes to 4.3 or 4.1 log(10) CFU/g, respectively. L. alimentariu s L-2 did not produce bacteriocins or hydrogen peroxide in vitro. The antilisterial effect of L. alimentarius observed in laboratory media a nd ground beef is attributed to lactic acid (ca. 50 mM) produced by gr owing cultures.