The inhibitory effect of probiotic Lactococcus lactis on the growth and invasion of Listeria monocytogenes in Caco-2 cell line

Listeria monocytogenes leads to listeriosis in humans through the consumption of ready-to-eat foods. Older adults, immunocompromised patients, pregnant women, and newborns are at the highest risk for this infection. To detect probiotic bacteria with an inhibitory activity against L. monocytogenes, we evaluated the inhibitory effect of Lactococcus lactis on the growth and invasion of L. monocytogenes.

In this study, we used the L. monocytogenes ATCC 7644 strain and the L. lactis PTCC 1336 probiotic strain. To investigate the inhibitory effects of L. lactis on the growth of pathogenic L. monocytogenes, we employed the well diffusion agar method, and to investigate its inhibitory effect on invasion by this bacterium, we conducted a co-culture with Caco-2 human enterocyte cells.

The results showed that L. lactis in concentrations of 0.25, 0.5, and 1 had antimicrobial properties against L. monocytogenes. With increasing concentration, the inhibitory effect on this pathogen increased. In addition, L. lactis showed an inhibitory effect on the L. monocytogenes invasion of Caco-2 cells. Therefore, in the concentration of 1, L. lactis decreased the number of bacteria by reducing the invasion of the cells by Listeria from log 108 to log 102; in the concentration of 0.5, from log 108 to log 103; and in the concentration of 0.25, from log 108 to log 105.

L. lactis has antimicrobial and inhibitory properties against the invasion of L. monocytogenes and can be considered an option to inhibit invasion and gastrointestinal infections caused by this bacterium.