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 beta. This approach may be useful to understand the mechanisms of microbial competition in food.

Automated summary

Studies have shown that lactic acid bacteria isolated from traditional cheeses produced in Calabria, Italy, have inhibitory effects on various spoilage and/or pathogenic microorganisms. Among them, strains 29, 31, and 76 (of Lactobacillus species) demonstrated the best performance in inhibiting Listeria monocytogenes, both in vitro and in soft cheese. These strains, with their technological characteristics taken into consideration, have the potential to be used as adjunct cultures to enhance the safety of finished products. The competition model proposed in the study, especially after incorporating the interspecific competition parameter beta, provided accurate predictions and may be valuable in understanding microbial competition mechanisms in food.