Bacteriocin exposure and food ingredients influence on growth and virulence of Listeria monocytogenes in a model meat gravy system

The antilisterial activity of bacteriocin-producing Lactobacillus sakei 1 bac(+) alone and combined with food ingredients (sodium chloride, D-glucose, oregano, black pepper) was studied in a model meat gravy (1.8% proteose peptone, 1.2% meat extract, 0.6% yeast extract, 2.0% corn starch) kept under refrigeration for 10 days. Two strains of L. monocytogenes (serotypes 4b and 1/2a) were employed in coinoculation experiments and Lactobacillus sakei ATCC 15521 was used as a negative control for bacteriocin production. The LAB bac(+) strain was more effective in inhibiting both L. monocytogenes serotypes than the LAB bac(-) strain. The serotype 4b was more sensitive to bacteriocin than serotype 1/2a. The effect of the ingredients on inhibition of L. monocytogenes was serotype dependent. Bacteriocin exposure did not affect sensitivity to ampicilin and rifampicin. However, L. monocytogenes partially lost their hemolytic activity after exposure to bacteriocin-producing Lb. sakei 1 and food ingredients.