Lactic acid bacteria isolated from traditional Italian dairy products: activity against Listeria monocytogenes and modelling of microbial competition in soft cheese

Several studies showed that lactic acid bacteria isolated from traditional cheeses produced in Calabria (Italy) inhibited in vitro the growth of different spoilage and/or pathogenic microorganisms. However, the activity of these autochthonous strains against Listeria monocytogenes has never been investigated. One hundred and fifteen lactic acid bacteria isolated from traditional Calabrian cheeses were screened for their technological characteristics and inhibiting action against Listeria monocytogenes in laboratory media. The anti-Listeria activity of representative strains was evaluated also in soft cheese during chilled storage. Bacterial interaction was studied using a competitive modelling approach based on Lotka-Volterra equations. Strains 29 (Lactobacillus sakei), 31 (Lactobacillus plantarum group), and 76 (Lactobacillus plantarum group) showed the best performances both in vitro and in soft cheese reducing the loads of Listeria monocytogenes from 0.5 to almost 1 Log CFU/g. Also considering their technological features, these strains could be used as adjunct cultures to improve the safety of finished products. The proposed competition model returned good predictions, especially after the application of the interspecific competition parameter β. This approach may be useful to understand the mechanisms of microbial competition in food.